From ad2ea3d3dd92a36e8a6377dd17da8601271995e5 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Sat, 14 Aug 2021 22:32:42 +0300
Subject: [PATCH 01/17] Annotate src

---
 .../src/ChainedConfigurationProvider.cs       |  7 ++--
 .../src/ChainedConfigurationSource.cs         |  2 +-
 .../src/ConfigurationKeyComparer.cs           |  2 +-
 .../src/ConfigurationManager.cs               |  5 ++-
 .../src/ConfigurationProvider.cs              | 15 ++++----
 .../src/ConfigurationReloadToken.cs           |  2 +-
 .../src/ConfigurationRoot.cs                  |  8 ++--
 .../src/ConfigurationSection.cs               | 38 +++++--------------
 .../InternalConfigurationRootExtensions.cs    |  2 +-
 .../MemoryConfigurationBuilderExtensions.cs   |  2 +-
 .../src/MemoryConfigurationProvider.cs        |  8 ++--
 .../src/MemoryConfigurationSource.cs          |  2 +-
 .../Microsoft.Extensions.Configuration.csproj | 10 ++++-
 .../src/StreamConfigurationProvider.cs        |  6 +++
 .../src/StreamConfigurationSource.cs          |  2 +-
 15 files changed, 54 insertions(+), 57 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
index a240f3da8e7d1..53e0660d067e0 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.Extensions.Configuration
@@ -40,7 +41,7 @@ public ChainedConfigurationProvider(ChainedConfigurationSource source)
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
         /// <returns><c>True</c> if a value for the specified key was found, otherwise <c>false</c>.</returns>
-        public bool TryGet(string key, out string value)
+        public bool TryGet(string key, [MaybeNullWhen(false)] out string value)
         {
             value = _config[key];
             return !string.IsNullOrEmpty(value);
@@ -51,7 +52,7 @@ public bool TryGet(string key, out string value)
         /// </summary>
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
-        public void Set(string key, string value) => _config[key] = value;
+        public void Set(string key, string? value) => _config[key] = value;
 
         /// <summary>
         /// Returns a change token if this provider supports change tracking, null otherwise.
@@ -74,7 +75,7 @@ public void Load() { }
         /// <returns>The child keys.</returns>
         public IEnumerable<string> GetChildKeys(
             IEnumerable<string> earlierKeys,
-            string parentPath)
+            string? parentPath)
         {
             IConfiguration section = parentPath == null ? _config : _config.GetSection(parentPath);
             var keys = new List<string>();
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationSource.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationSource.cs
index 27391aead76fd..adab1de349a6c 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationSource.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationSource.cs
@@ -11,7 +11,7 @@ public class ChainedConfigurationSource : IConfigurationSource
         /// <summary>
         /// The chained configuration.
         /// </summary>
-        public IConfiguration Configuration { get; set; }
+        public IConfiguration? Configuration { get; set; }
 
         /// <summary>
         /// Whether the chained configuration should be disposed when the
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
index b5dc31fdffe73..00cca781d47f4 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
@@ -27,7 +27,7 @@ public class ConfigurationKeyComparer : IComparer<string>
         /// <param name="x">First string.</param>
         /// <param name="y">Second string.</param>
         /// <returns>Less than 0 if x is less than y, 0 if x is equal to y and greater than 0 if x is greater than y.</returns>
-        public int Compare(string x, string y)
+        public int Compare(string? x, string? y)
         {
             string[] xParts = x?.Split(_keyDelimiterArray, StringSplitOptions.RemoveEmptyEntries) ?? Array.Empty<string>();
             string[] yParts = y?.Split(_keyDelimiterArray, StringSplitOptions.RemoveEmptyEntries) ?? Array.Empty<string>();
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationManager.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationManager.cs
index 9578f3c334ac3..db1d682a9464a 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationManager.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationManager.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Threading;
 using Microsoft.Extensions.Primitives;
@@ -39,7 +40,7 @@ public ConfigurationManager()
         }
 
         /// <inheritdoc/>
-        public string this[string key]
+        public string? this[string key]
         {
             get
             {
@@ -339,7 +340,7 @@ public bool Remove(KeyValuePair<string, object> item)
                 return wasRemoved;
             }
 
-            public bool TryGetValue(string key, out object value)
+            public bool TryGetValue(string key, [MaybeNullWhen(false)] out object value)
             {
                 return _properties.TryGetValue(key, out value);
             }
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
index e337bd3148331..e3eb4f977bffc 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.Extensions.Primitives;
 
@@ -21,13 +22,13 @@ public abstract class ConfigurationProvider : IConfigurationProvider
         /// </summary>
         protected ConfigurationProvider()
         {
-            Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+            Data = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
         }
 
         /// <summary>
         /// The configuration key value pairs for this provider.
         /// </summary>
-        protected IDictionary<string, string> Data { get; set; }
+        protected IDictionary<string, string?> Data { get; set; }
 
         /// <summary>
         /// Attempts to find a value with the given key, returns true if one is found, false otherwise.
@@ -35,7 +36,7 @@ protected ConfigurationProvider()
         /// <param name="key">The key to lookup.</param>
         /// <param name="value">The value found at key if one is found.</param>
         /// <returns>True if key has a value, false otherwise.</returns>
-        public virtual bool TryGet(string key, out string value)
+        public virtual bool TryGet(string key, [MaybeNullWhen(false)] out string value)
             => Data.TryGetValue(key, out value);
 
         /// <summary>
@@ -43,7 +44,7 @@ public virtual bool TryGet(string key, out string value)
         /// </summary>
         /// <param name="key">The configuration key to set.</param>
         /// <param name="value">The value to set.</param>
-        public virtual void Set(string key, string value)
+        public virtual void Set(string key, string? value)
             => Data[key] = value;
 
         /// <summary>
@@ -60,13 +61,13 @@ public virtual void Load()
         /// <returns>The list of keys for this provider.</returns>
         public virtual IEnumerable<string> GetChildKeys(
             IEnumerable<string> earlierKeys,
-            string parentPath)
+            string? parentPath)
         {
             var results = new List<string>();
 
             if (parentPath is null)
             {
-                foreach (KeyValuePair<string, string> kv in Data)
+                foreach (KeyValuePair<string, string?> kv in Data)
                 {
                     results.Add(Segment(kv.Key, 0));
                 }
@@ -75,7 +76,7 @@ public virtual IEnumerable<string> GetChildKeys(
             {
                 Debug.Assert(ConfigurationPath.KeyDelimiter == ":");
 
-                foreach (KeyValuePair<string, string> kv in Data)
+                foreach (KeyValuePair<string, string?> kv in Data)
                 {
                     if (kv.Key.Length > parentPath.Length &&
                         kv.Key.StartsWith(parentPath, StringComparison.OrdinalIgnoreCase) &&
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
index fad07ebfdacb9..7aceba29fe55b 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
@@ -33,7 +33,7 @@ public class ConfigurationReloadToken : IChangeToken
         /// <param name="callback">The callback to invoke.</param>
         /// <param name="state">State to be passed into the callback.</param>
         /// <returns>The <see cref="CancellationToken"/> registration.</returns>
-        public IDisposable RegisterChangeCallback(Action<object> callback, object state) => _cts.Token.Register(callback, state);
+        public IDisposable RegisterChangeCallback(Action<object?> callback, object? state) => _cts.Token.Register(callback, state);
 
         /// <summary>
         /// Used to trigger the change token when a reload occurs.
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
index cfe56a20978e5..397ef5160b1ec 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
@@ -47,7 +47,7 @@ public ConfigurationRoot(IList<IConfigurationProvider> providers)
         /// </summary>
         /// <param name="key">The configuration key.</param>
         /// <returns>The configuration value.</returns>
-        public string this[string key]
+        public string? this[string key]
         {
             get => GetConfiguration(_providers, key);
             set => SetConfiguration(_providers, key, value);
@@ -111,13 +111,13 @@ public void Dispose()
             }
         }
 
-        internal static string GetConfiguration(IList<IConfigurationProvider> providers, string key)
+        internal static string? GetConfiguration(IList<IConfigurationProvider> providers, string key)
         {
             for (int i = providers.Count - 1; i >= 0; i--)
             {
                 IConfigurationProvider provider = providers[i];
 
-                if (provider.TryGet(key, out string value))
+                if (provider.TryGet(key, out string? value))
                 {
                     return value;
                 }
@@ -126,7 +126,7 @@ internal static string GetConfiguration(IList<IConfigurationProvider> providers,
             return null;
         }
 
-        internal static void SetConfiguration(IList<IConfigurationProvider> providers, string key, string value)
+        internal static void SetConfiguration(IList<IConfigurationProvider> providers, string key, string? value)
         {
             if (providers.Count == 0)
             {
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationSection.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationSection.cs
index da3fbb733a3a1..411b0d70fd765 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationSection.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationSection.cs
@@ -14,7 +14,7 @@ public class ConfigurationSection : IConfigurationSection
     {
         private readonly IConfigurationRoot _root;
         private readonly string _path;
-        private string _key;
+        private string? _key;
 
         /// <summary>
         /// Initializes a new instance.
@@ -47,30 +47,17 @@ public ConfigurationSection(IConfigurationRoot root, string path)
         /// </summary>
         public string Key
         {
-            get
-            {
-                if (_key == null)
-                {
-                    // Key is calculated lazily as last portion of Path
-                    _key = ConfigurationPath.GetSectionKey(_path);
-                }
-                return _key;
-            }
+            // Key is calculated lazily as last portion of Path
+            get => _key ??= ConfigurationPath.GetSectionKey(_path);
         }
 
         /// <summary>
         /// Gets or sets the section value.
         /// </summary>
-        public string Value
+        public string? Value
         {
-            get
-            {
-                return _root[Path];
-            }
-            set
-            {
-                _root[Path] = value;
-            }
+            get => _root[Path];
+            set => _root[Path] = value;
         }
 
         /// <summary>
@@ -78,17 +65,10 @@ public string Value
         /// </summary>
         /// <param name="key">The configuration key.</param>
         /// <returns>The configuration value.</returns>
-        public string this[string key]
+        public string? this[string key]
         {
-            get
-            {
-                return _root[ConfigurationPath.Combine(Path, key)];
-            }
-
-            set
-            {
-                _root[ConfigurationPath.Combine(Path, key)] = value;
-            }
+            get => _root[ConfigurationPath.Combine(Path, key)];
+            set => _root[ConfigurationPath.Combine(Path, key)] = value;
         }
 
         /// <summary>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/InternalConfigurationRootExtensions.cs b/src/libraries/Microsoft.Extensions.Configuration/src/InternalConfigurationRootExtensions.cs
index bff5c52710400..7fd17a98acf47 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/InternalConfigurationRootExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/InternalConfigurationRootExtensions.cs
@@ -18,7 +18,7 @@ internal static class InternalConfigurationRootExtensions
         /// <param name="root">Configuration from which to retrieve sub-sections.</param>
         /// <param name="path">Key of a section of which children to retrieve.</param>
         /// <returns>Immediate children sub-sections of section specified by key.</returns>
-        internal static IEnumerable<IConfigurationSection> GetChildrenImplementation(this IConfigurationRoot root, string path)
+        internal static IEnumerable<IConfigurationSection> GetChildrenImplementation(this IConfigurationRoot root, string? path)
         {
             return root.Providers
                 .Aggregate(Enumerable.Empty<string>(),
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationBuilderExtensions.cs b/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationBuilderExtensions.cs
index 996f8a876b9c3..15ed46a26a5b9 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationBuilderExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationBuilderExtensions.cs
@@ -36,7 +36,7 @@ public static IConfigurationBuilder AddInMemoryCollection(this IConfigurationBui
         /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
         public static IConfigurationBuilder AddInMemoryCollection(
             this IConfigurationBuilder configurationBuilder,
-            IEnumerable<KeyValuePair<string, string>> initialData)
+            IEnumerable<KeyValuePair<string, string?>>? initialData)
         {
             if (configurationBuilder == null)
             {
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationProvider.cs
index 84a0b142e0fbc..0e7f0be02fec7 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationProvider.cs
@@ -10,7 +10,7 @@ namespace Microsoft.Extensions.Configuration.Memory
     /// <summary>
     /// In-memory implementation of <see cref="IConfigurationProvider"/>
     /// </summary>
-    public class MemoryConfigurationProvider : ConfigurationProvider, IEnumerable<KeyValuePair<string, string>>
+    public class MemoryConfigurationProvider : ConfigurationProvider, IEnumerable<KeyValuePair<string, string?>>
     {
         private readonly MemoryConfigurationSource _source;
 
@@ -29,7 +29,7 @@ public MemoryConfigurationProvider(MemoryConfigurationSource source)
 
             if (_source.InitialData != null)
             {
-                foreach (KeyValuePair<string, string> pair in _source.InitialData)
+                foreach (KeyValuePair<string, string?> pair in _source.InitialData)
                 {
                     Data.Add(pair.Key, pair.Value);
                 }
@@ -41,7 +41,7 @@ public MemoryConfigurationProvider(MemoryConfigurationSource source)
         /// </summary>
         /// <param name="key">The configuration key.</param>
         /// <param name="value">The configuration value.</param>
-        public void Add(string key, string value)
+        public void Add(string key, string? value)
         {
             Data.Add(key, value);
         }
@@ -50,7 +50,7 @@ public void Add(string key, string value)
         /// Returns an enumerator that iterates through the collection.
         /// </summary>
         /// <returns>An enumerator that can be used to iterate through the collection.</returns>
-        public IEnumerator<KeyValuePair<string, string>> GetEnumerator()
+        public IEnumerator<KeyValuePair<string, string?>> GetEnumerator()
         {
             return Data.GetEnumerator();
         }
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationSource.cs b/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationSource.cs
index e11891595e414..412df6534c110 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationSource.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/MemoryConfigurationSource.cs
@@ -13,7 +13,7 @@ public class MemoryConfigurationSource : IConfigurationSource
         /// <summary>
         /// The initial key value configuration pairs.
         /// </summary>
-        public IEnumerable<KeyValuePair<string, string>> InitialData { get; set; }
+        public IEnumerable<KeyValuePair<string, string?>>? InitialData { get; set; }
 
         /// <summary>
         /// Builds the <see cref="MemoryConfigurationProvider"/> for this source.
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj b/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
index 62243f8db8537..e8093696ecba9 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
+    <Nullable>enable</Nullable>
     <EnableDefaultItems>true</EnableDefaultItems>
     <PackageDescription>Implementation of key-value pair based configuration for Microsoft.Extensions.Configuration. Includes the memory configuration provider.</PackageDescription>
   </PropertyGroup>
@@ -11,4 +12,11 @@
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
+    <Reference Include="System.Linq" />
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Collections" />
+    <Reference Include="System.Threading" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
index fb279be1b4c5f..0b18569818c73 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
@@ -42,6 +42,12 @@ public override void Load()
             {
                 throw new InvalidOperationException(SR.StreamConfigurationProvidersAlreadyLoaded);
             }
+
+            if (Source.Stream == null)
+            {
+                throw new NullReferenceException("Source.Stream");
+            }
+
             Load(Source.Stream);
             _loaded = true;
         }
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationSource.cs b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationSource.cs
index 3fdf741443509..a658ba74f1dcb 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationSource.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationSource.cs
@@ -13,7 +13,7 @@ public abstract class StreamConfigurationSource : IConfigurationSource
         /// <summary>
         /// The stream containing the configuration data.
         /// </summary>
-        public Stream Stream { get; set; }
+        public Stream? Stream { get; set; }
 
         /// <summary>
         /// Builds the <see cref="StreamConfigurationProvider"/> for this source.

From 04bc30b327a0cb1a1e203ee17d122c3f33c4882c Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Sat, 14 Aug 2021 22:46:08 +0300
Subject: [PATCH 02/17] Annotate ref

---
 .../ref/Microsoft.Extensions.Configuration.cs | 38 +++++++++----------
 .../Microsoft.Extensions.Configuration.csproj |  9 ++++-
 2 files changed, 27 insertions(+), 20 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
index feef64fc2dde1..8590771e42fb2 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
@@ -15,23 +15,23 @@ public partial class ChainedConfigurationProvider : Microsoft.Extensions.Configu
     {
         public ChainedConfigurationProvider(Microsoft.Extensions.Configuration.ChainedConfigurationSource source) { }
         public void Dispose() { }
-        public System.Collections.Generic.IEnumerable<string> GetChildKeys(System.Collections.Generic.IEnumerable<string> earlierKeys, string parentPath) { throw null; }
+        public System.Collections.Generic.IEnumerable<string> GetChildKeys(System.Collections.Generic.IEnumerable<string> earlierKeys, string? parentPath) { throw null; }
         public Microsoft.Extensions.Primitives.IChangeToken GetReloadToken() { throw null; }
         public void Load() { }
-        public void Set(string key, string value) { }
-        public bool TryGet(string key, out string value) { throw null; }
+        public void Set(string key, string? value) { }
+        public bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value) { throw null; }
     }
     public partial class ChainedConfigurationSource : Microsoft.Extensions.Configuration.IConfigurationSource
     {
         public ChainedConfigurationSource() { }
-        public Microsoft.Extensions.Configuration.IConfiguration Configuration { get { throw null; } set { } }
+        public Microsoft.Extensions.Configuration.IConfiguration? Configuration { get { throw null; } set { } }
         public bool ShouldDisposeConfiguration { get { throw null; } set { } }
         public Microsoft.Extensions.Configuration.IConfigurationProvider Build(Microsoft.Extensions.Configuration.IConfigurationBuilder builder) { throw null; }
     }
     public sealed partial class ConfigurationManager : Microsoft.Extensions.Configuration.IConfigurationBuilder, Microsoft.Extensions.Configuration.IConfigurationRoot, System.IDisposable
     {
         public ConfigurationManager() { }
-        public string this[string key] { get { throw null; } set { throw null; } }
+        public string? this[string key] { get { throw null; } set { throw null; } }
         public IConfigurationSection GetSection(string key) { throw null; }
         public System.Collections.Generic.IEnumerable<IConfigurationSection> GetChildren() { throw null; }
         public void Dispose() { throw null; }
@@ -55,19 +55,19 @@ public partial class ConfigurationKeyComparer : System.Collections.Generic.IComp
     {
         public ConfigurationKeyComparer() { }
         public static Microsoft.Extensions.Configuration.ConfigurationKeyComparer Instance { get { throw null; } }
-        public int Compare(string x, string y) { throw null; }
+        public int Compare(string? x, string? y) { throw null; }
     }
     public abstract partial class ConfigurationProvider : Microsoft.Extensions.Configuration.IConfigurationProvider
     {
         protected ConfigurationProvider() { }
-        protected System.Collections.Generic.IDictionary<string, string> Data { get { throw null; } set { } }
-        public virtual System.Collections.Generic.IEnumerable<string> GetChildKeys(System.Collections.Generic.IEnumerable<string> earlierKeys, string parentPath) { throw null; }
+        protected System.Collections.Generic.IDictionary<string, string?> Data { get { throw null; } set { } }
+        public virtual System.Collections.Generic.IEnumerable<string> GetChildKeys(System.Collections.Generic.IEnumerable<string> earlierKeys, string? parentPath) { throw null; }
         public Microsoft.Extensions.Primitives.IChangeToken GetReloadToken() { throw null; }
         public virtual void Load() { }
         protected void OnReload() { }
-        public virtual void Set(string key, string value) { }
+        public virtual void Set(string key, string? value) { }
         public override string ToString() { throw null; }
-        public virtual bool TryGet(string key, out string value) { throw null; }
+        public virtual bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value) { throw null; }
     }
     public partial class ConfigurationReloadToken : Microsoft.Extensions.Primitives.IChangeToken
     {
@@ -75,12 +75,12 @@ public ConfigurationReloadToken() { }
         public bool ActiveChangeCallbacks { get { throw null; } }
         public bool HasChanged { get { throw null; } }
         public void OnReload() { }
-        public System.IDisposable RegisterChangeCallback(System.Action<object> callback, object state) { throw null; }
+        public System.IDisposable RegisterChangeCallback(System.Action<object?> callback, object? state) { throw null; }
     }
     public partial class ConfigurationRoot : Microsoft.Extensions.Configuration.IConfiguration, Microsoft.Extensions.Configuration.IConfigurationRoot, System.IDisposable
     {
         public ConfigurationRoot(System.Collections.Generic.IList<Microsoft.Extensions.Configuration.IConfigurationProvider> providers) { }
-        public string this[string key] { get { throw null; } set { } }
+        public string? this[string key] { get { throw null; } set { } }
         public System.Collections.Generic.IEnumerable<Microsoft.Extensions.Configuration.IConfigurationProvider> Providers { get { throw null; } }
         public void Dispose() { }
         public System.Collections.Generic.IEnumerable<Microsoft.Extensions.Configuration.IConfigurationSection> GetChildren() { throw null; }
@@ -91,10 +91,10 @@ public void Reload() { }
     public partial class ConfigurationSection : Microsoft.Extensions.Configuration.IConfiguration, Microsoft.Extensions.Configuration.IConfigurationSection
     {
         public ConfigurationSection(Microsoft.Extensions.Configuration.IConfigurationRoot root, string path) { }
-        public string this[string key] { get { throw null; } set { } }
+        public string? this[string key] { get { throw null; } set { } }
         public string Key { get { throw null; } }
         public string Path { get { throw null; } }
-        public string Value { get { throw null; } set { } }
+        public string? Value { get { throw null; } set { } }
         public System.Collections.Generic.IEnumerable<Microsoft.Extensions.Configuration.IConfigurationSection> GetChildren() { throw null; }
         public Microsoft.Extensions.Primitives.IChangeToken GetReloadToken() { throw null; }
         public Microsoft.Extensions.Configuration.IConfigurationSection GetSection(string key) { throw null; }
@@ -102,7 +102,7 @@ public ConfigurationSection(Microsoft.Extensions.Configuration.IConfigurationRoo
     public static partial class MemoryConfigurationBuilderExtensions
     {
         public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddInMemoryCollection(this Microsoft.Extensions.Configuration.IConfigurationBuilder configurationBuilder) { throw null; }
-        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddInMemoryCollection(this Microsoft.Extensions.Configuration.IConfigurationBuilder configurationBuilder, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string>> initialData) { throw null; }
+        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddInMemoryCollection(this Microsoft.Extensions.Configuration.IConfigurationBuilder configurationBuilder, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string?>>? initialData) { throw null; }
     }
     public abstract partial class StreamConfigurationProvider : Microsoft.Extensions.Configuration.ConfigurationProvider
     {
@@ -120,17 +120,17 @@ protected StreamConfigurationSource() { }
 }
 namespace Microsoft.Extensions.Configuration.Memory
 {
-    public partial class MemoryConfigurationProvider : Microsoft.Extensions.Configuration.ConfigurationProvider, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string>>, System.Collections.IEnumerable
+    public partial class MemoryConfigurationProvider : Microsoft.Extensions.Configuration.ConfigurationProvider, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string?>>, System.Collections.IEnumerable
     {
         public MemoryConfigurationProvider(Microsoft.Extensions.Configuration.Memory.MemoryConfigurationSource source) { }
-        public void Add(string key, string value) { }
-        public System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string, string>> GetEnumerator() { throw null; }
+        public void Add(string key, string? value) { }
+        public System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string, string?>> GetEnumerator() { throw null; }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
     }
     public partial class MemoryConfigurationSource : Microsoft.Extensions.Configuration.IConfigurationSource
     {
         public MemoryConfigurationSource() { }
-        public System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string>> InitialData { get { throw null; } set { } }
+        public System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string?>>? InitialData { get { throw null; } set { } }
         public Microsoft.Extensions.Configuration.IConfigurationProvider Build(Microsoft.Extensions.Configuration.IConfigurationBuilder builder) { throw null; }
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
index e1533c3eadf9e..dd5d096ce7fc5 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
@@ -1,10 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.cs" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
+    <Reference Include="System.Linq" />
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Collections" />
+    <Reference Include="System.Threading" />
+  </ItemGroup>
 </Project>

From 65f47b21aebc89bfa2d4a23c8949aded4cce3121 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Sat, 14 Aug 2021 23:45:56 +0300
Subject: [PATCH 03/17] Add net6 to Configuration.Abstractions

---
 .../Microsoft.Extensions.Configuration.Abstractions.csproj | 6 ++++++
 .../Microsoft.Extensions.Configuration.Abstractions.csproj | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
index d6b7d921c7a1e..b9944f036eb8b 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.Abstractions.cs" />
@@ -8,4 +9,9 @@
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
+    <Reference Include="System.Linq" />
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Collections" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
index 24cbc9380f00f..7c1ef3d63034a 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <PackageDescription>Abstractions of key-value pair based configuration.
 
@@ -21,4 +22,10 @@ Microsoft.Extensions.Configuration.IConfigurationSection</PackageDescription>
     <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
+    <Reference Include="System.Linq" />
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Collections" />
+  </ItemGroup>
+
 </Project>

From 44d0ac0e1455046a8d98c3302c1ea36873b7f88f Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Sun, 15 Aug 2021 00:35:58 +0300
Subject: [PATCH 04/17] Fix tests

---
 .../tests/OptionsBuidlerConfigurationExtensionsTests.cs   | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/OptionsBuidlerConfigurationExtensionsTests.cs b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/OptionsBuidlerConfigurationExtensionsTests.cs
index 9d4764c19c0b4..387beac8cc434 100644
--- a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/OptionsBuidlerConfigurationExtensionsTests.cs
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/OptionsBuidlerConfigurationExtensionsTests.cs
@@ -66,7 +66,7 @@ public static void BindConfiguration_UsesConfigurationSectionPath()
         {
             const string configSectionName = "Test";
             const string messageValue = "This is a test";
-            var configEntries = new Dictionary<string, string>
+            var configEntries = new Dictionary<string, string?>
             {
                 [ConfigurationPath.Combine(configSectionName, nameof(FakeOptions.Message))] = messageValue
             };
@@ -88,7 +88,7 @@ public static void BindConfiguration_UsesConfigurationSectionPath()
         public static void BindConfiguration_UsesConfigurationRootIfSectionNameIsEmptyString()
         {
             const string messageValue = "This is a test";
-            var configEntries = new Dictionary<string, string>
+            var configEntries = new Dictionary<string, string?>
             {
                 [nameof(FakeOptions.Message)] = messageValue
             };
@@ -114,7 +114,7 @@ public static void BindConfiguration_UpdatesOptionOnConfigurationUpdateWithEmpty
 
             FakeConfigurationSource configSource = new()
             {
-                InitialData = new Dictionary<string, string>
+                InitialData = new Dictionary<string, string?>
                 {
                     [nameof(FakeOptions.Message)] = messageValue1,
                 }
@@ -151,7 +151,7 @@ public static void BindConfiguration_UpdatesOptionOnConfigurationUpdate()
 
             FakeConfigurationSource configSource = new()
             {
-                InitialData = new Dictionary<string, string>
+                InitialData = new Dictionary<string, string?>
                 {
                     [messageConfigKey] = messageValue1
                 }

From 5a7a6d3956480165cddbed2518f21109b0de62eb Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Fri, 27 Aug 2021 00:52:34 +0300
Subject: [PATCH 05/17] DisableImplicitAssemblyReferences

---
 .../ref/Microsoft.Extensions.Configuration.csproj        | 6 ++----
 .../src/Microsoft.Extensions.Configuration.csproj        | 9 ++-------
 2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
index dd5d096ce7fc5..f3eff1d87e49d 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
@@ -9,9 +9,7 @@
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Threading" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections\ref\System.Collections.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj b/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
index e8093696ecba9..6137de44b42f3 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
@@ -4,6 +4,8 @@
     <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
     <EnableDefaultItems>true</EnableDefaultItems>
+    <!-- Use targeting pack references instead of granular ones in the project file. -->
+    <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
     <PackageDescription>Implementation of key-value pair based configuration for Microsoft.Extensions.Configuration. Includes the memory configuration provider.</PackageDescription>
   </PropertyGroup>
 
@@ -12,11 +14,4 @@
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Threading" />
-  </ItemGroup>
-
 </Project>

From 4945112a33c43d03f882bff6abb4a62977f8b990 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Thu, 16 Sep 2021 17:41:46 +0300
Subject: [PATCH 06/17] TryGet can return null

---
 .../ref/Microsoft.Extensions.Configuration.cs                  | 2 +-
 .../src/ConfigurationProvider.cs                               | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
index 8590771e42fb2..65da073c427be 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
@@ -67,7 +67,7 @@ public virtual void Load() { }
         protected void OnReload() { }
         public virtual void Set(string key, string? value) { }
         public override string ToString() { throw null; }
-        public virtual bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value) { throw null; }
+        public virtual bool TryGet(string key, out string? value) { throw null; }
     }
     public partial class ConfigurationReloadToken : Microsoft.Extensions.Primitives.IChangeToken
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
index e3eb4f977bffc..9fbeded4fc3de 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.Extensions.Primitives;
 
@@ -36,7 +35,7 @@ protected ConfigurationProvider()
         /// <param name="key">The key to lookup.</param>
         /// <param name="value">The value found at key if one is found.</param>
         /// <returns>True if key has a value, false otherwise.</returns>
-        public virtual bool TryGet(string key, [MaybeNullWhen(false)] out string value)
+        public virtual bool TryGet(string key, out string? value)
             => Data.TryGetValue(key, out value);
 
         /// <summary>

From f320ed0265041858aeb95f60fe024c13a75f3d23 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Thu, 16 Sep 2021 17:48:38 +0300
Subject: [PATCH 07/17] new()

---
 .../src/ConfigurationKeyComparer.cs                             | 2 +-
 .../src/ConfigurationProvider.cs                                | 2 +-
 .../src/ConfigurationReloadToken.cs                             | 2 +-
 .../Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
index 00cca781d47f4..981814642c440 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
@@ -16,7 +16,7 @@ public class ConfigurationKeyComparer : IComparer<string>
         /// <summary>
         /// The default instance.
         /// </summary>
-        public static ConfigurationKeyComparer Instance { get; } = new ConfigurationKeyComparer();
+        public static ConfigurationKeyComparer Instance { get; } = new();
 
         /// <summary>A comparer delegate with the default instance.</summary>
         internal static Comparison<string> Comparison { get; } = Instance.Compare;
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
index 9fbeded4fc3de..55d7adcd9f1df 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
@@ -14,7 +14,7 @@ namespace Microsoft.Extensions.Configuration
     /// </summary>
     public abstract class ConfigurationProvider : IConfigurationProvider
     {
-        private ConfigurationReloadToken _reloadToken = new ConfigurationReloadToken();
+        private ConfigurationReloadToken _reloadToken = new();
 
         /// <summary>
         /// Initializes a new <see cref="IConfigurationProvider"/>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
index 7aceba29fe55b..0da3b1c5508f5 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
@@ -12,7 +12,7 @@ namespace Microsoft.Extensions.Configuration
     /// </summary>
     public class ConfigurationReloadToken : IChangeToken
     {
-        private CancellationTokenSource _cts = new CancellationTokenSource();
+        private CancellationTokenSource _cts = new();
 
         /// <summary>
         /// Indicates if this token will proactively raise callbacks. Callbacks are still guaranteed to be invoked, eventually.
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
index 397ef5160b1ec..c666372dd25cf 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
@@ -15,7 +15,7 @@ public class ConfigurationRoot : IConfigurationRoot, IDisposable
     {
         private readonly IList<IConfigurationProvider> _providers;
         private readonly IList<IDisposable> _changeTokenRegistrations;
-        private ConfigurationReloadToken _changeToken = new ConfigurationReloadToken();
+        private ConfigurationReloadToken _changeToken = new();
 
         /// <summary>
         /// Initializes a Configuration root with a list of providers.

From b9a0a93e4d659947624b39b6f61c5762c8d43156 Mon Sep 17 00:00:00 2001
From: Eric Erhardt <eric.erhardt@microsoft.com>
Date: Wed, 6 Oct 2021 16:23:48 -0500
Subject: [PATCH 08/17] Fix merge error

---
 .../Microsoft.Extensions.Configuration.Abstractions.csproj  | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
index 3a707795afacf..49aabd359e3fc 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
@@ -24,10 +24,4 @@ Microsoft.Extensions.Configuration.IConfigurationSection</PackageDescription>
     <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Collections" />
-  </ItemGroup>
-
 </Project>

From e5228aa33c36970f77b2f4a3eaa9cc113fa70cea Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Thu, 7 Oct 2021 09:17:41 +0300
Subject: [PATCH 09/17] InvalidOperationException

---
 .../src/StreamConfigurationProvider.cs                          | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
index 0b18569818c73..0fe206f3c5415 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
@@ -45,7 +45,7 @@ public override void Load()
 
             if (Source.Stream == null)
             {
-                throw new NullReferenceException("Source.Stream");
+                throw new InvalidOperationException("Source.Stream cannot be null");
             }
 
             Load(Source.Stream);

From 1c583ecef83e9e3e22f0c7d90fc8f14416cb3ee7 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Thu, 7 Oct 2021 09:30:56 +0300
Subject: [PATCH 10/17] Source.Stream DisallowNull

---
 .../ref/Microsoft.Extensions.Configuration.cs                  | 3 ++-
 .../src/StreamConfigurationSource.cs                           | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
index 65da073c427be..e9eada6e0ad2f 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
@@ -114,7 +114,8 @@ public override void Load() { }
     public abstract partial class StreamConfigurationSource : Microsoft.Extensions.Configuration.IConfigurationSource
     {
         protected StreamConfigurationSource() { }
-        public System.IO.Stream Stream { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.DisallowNull]
+        public System.IO.Stream? Stream { get { throw null; } set { } }
         public abstract Microsoft.Extensions.Configuration.IConfigurationProvider Build(Microsoft.Extensions.Configuration.IConfigurationBuilder builder);
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationSource.cs b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationSource.cs
index a658ba74f1dcb..f857b9b313d00 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationSource.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationSource.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 
 namespace Microsoft.Extensions.Configuration
@@ -13,6 +14,7 @@ public abstract class StreamConfigurationSource : IConfigurationSource
         /// <summary>
         /// The stream containing the configuration data.
         /// </summary>
+        [DisallowNull]
         public Stream? Stream { get; set; }
 
         /// <summary>

From a45a8217121a44b44aada985560dcf9817289feb Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Fri, 8 Oct 2021 18:12:30 +0300
Subject: [PATCH 11/17] Revert unnecessary changes

---
 .../src/ConfigurationKeyComparer.cs           |  2 +-
 .../src/ConfigurationProvider.cs              |  2 +-
 .../src/ConfigurationReloadToken.cs           |  2 +-
 .../src/ConfigurationRoot.cs                  |  2 +-
 .../src/ConfigurationSection.cs               | 31 +++++++++++++++----
 5 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
index 981814642c440..00cca781d47f4 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationKeyComparer.cs
@@ -16,7 +16,7 @@ public class ConfigurationKeyComparer : IComparer<string>
         /// <summary>
         /// The default instance.
         /// </summary>
-        public static ConfigurationKeyComparer Instance { get; } = new();
+        public static ConfigurationKeyComparer Instance { get; } = new ConfigurationKeyComparer();
 
         /// <summary>A comparer delegate with the default instance.</summary>
         internal static Comparison<string> Comparison { get; } = Instance.Compare;
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
index 55d7adcd9f1df..9fbeded4fc3de 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
@@ -14,7 +14,7 @@ namespace Microsoft.Extensions.Configuration
     /// </summary>
     public abstract class ConfigurationProvider : IConfigurationProvider
     {
-        private ConfigurationReloadToken _reloadToken = new();
+        private ConfigurationReloadToken _reloadToken = new ConfigurationReloadToken();
 
         /// <summary>
         /// Initializes a new <see cref="IConfigurationProvider"/>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
index 0da3b1c5508f5..7aceba29fe55b 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs
@@ -12,7 +12,7 @@ namespace Microsoft.Extensions.Configuration
     /// </summary>
     public class ConfigurationReloadToken : IChangeToken
     {
-        private CancellationTokenSource _cts = new();
+        private CancellationTokenSource _cts = new CancellationTokenSource();
 
         /// <summary>
         /// Indicates if this token will proactively raise callbacks. Callbacks are still guaranteed to be invoked, eventually.
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
index c666372dd25cf..397ef5160b1ec 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationRoot.cs
@@ -15,7 +15,7 @@ public class ConfigurationRoot : IConfigurationRoot, IDisposable
     {
         private readonly IList<IConfigurationProvider> _providers;
         private readonly IList<IDisposable> _changeTokenRegistrations;
-        private ConfigurationReloadToken _changeToken = new();
+        private ConfigurationReloadToken _changeToken = new ConfigurationReloadToken();
 
         /// <summary>
         /// Initializes a Configuration root with a list of providers.
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationSection.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationSection.cs
index 411b0d70fd765..0896e587d4082 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationSection.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationSection.cs
@@ -47,8 +47,15 @@ public ConfigurationSection(IConfigurationRoot root, string path)
         /// </summary>
         public string Key
         {
-            // Key is calculated lazily as last portion of Path
-            get => _key ??= ConfigurationPath.GetSectionKey(_path);
+            get
+            {
+                if (_key == null)
+                {
+                    // Key is calculated lazily as last portion of Path
+                    _key = ConfigurationPath.GetSectionKey(_path);
+                }
+                return _key;
+            }
         }
 
         /// <summary>
@@ -56,8 +63,14 @@ public string Key
         /// </summary>
         public string? Value
         {
-            get => _root[Path];
-            set => _root[Path] = value;
+            get
+            {
+                return _root[Path];
+            }
+            set
+            {
+                _root[Path] = value;
+            }
         }
 
         /// <summary>
@@ -67,8 +80,14 @@ public string? Value
         /// <returns>The configuration value.</returns>
         public string? this[string key]
         {
-            get => _root[ConfigurationPath.Combine(Path, key)];
-            set => _root[ConfigurationPath.Combine(Path, key)] = value;
+            get
+            {
+                return _root[ConfigurationPath.Combine(Path, key)];
+            }
+            set
+            {
+                _root[ConfigurationPath.Combine(Path, key)] = value;
+            }
         }
 
         /// <summary>

From d33438a35fc6b1876e5c190e9a562ad70a4270f8 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Fri, 8 Oct 2021 18:34:17 +0300
Subject: [PATCH 12/17] More message into resources

---
 .../src/Resources/Strings.resx                               | 5 ++++-
 .../src/StreamConfigurationProvider.cs                       | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/Resources/Strings.resx b/src/libraries/Microsoft.Extensions.Configuration/src/Resources/Strings.resx
index 941bf0cc34873..8f6038211e50d 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/Resources/Strings.resx
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/Resources/Strings.resx
@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <root>
   <!-- 
     Microsoft ResX Schema 
@@ -126,4 +126,7 @@
   <data name="StreamConfigurationProvidersAlreadyLoaded" xml:space="preserve">
     <value>StreamConfigurationProviders cannot be loaded more than once.</value>
   </data>
+  <data name="StreamConfigurationSourceStreamCannotBeNull" xml:space="preserve">
+    <value>Source.Stream cannot be null.</value>
+  </data>
 </root>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
index 0fe206f3c5415..6d8917a188fd6 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/StreamConfigurationProvider.cs
@@ -45,7 +45,7 @@ public override void Load()
 
             if (Source.Stream == null)
             {
-                throw new InvalidOperationException("Source.Stream cannot be null");
+                throw new InvalidOperationException(SR.StreamConfigurationSourceStreamCannotBeNull);
             }
 
             Load(Source.Stream);

From 2ca692ab8a1dd962aa5088c80fdf3e02d3ecc30f Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Fri, 8 Oct 2021 18:55:46 +0300
Subject: [PATCH 13/17] Configuration DisallowNull

---
 .../ref/Microsoft.Extensions.Configuration.cs                  | 1 +
 .../src/ChainedConfigurationSource.cs                          | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
index e9eada6e0ad2f..73e24b774c393 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
@@ -24,6 +24,7 @@ public void Set(string key, string? value) { }
     public partial class ChainedConfigurationSource : Microsoft.Extensions.Configuration.IConfigurationSource
     {
         public ChainedConfigurationSource() { }
+        [System.Diagnostics.CodeAnalysis.DisallowNull]
         public Microsoft.Extensions.Configuration.IConfiguration? Configuration { get { throw null; } set { } }
         public bool ShouldDisposeConfiguration { get { throw null; } set { } }
         public Microsoft.Extensions.Configuration.IConfigurationProvider Build(Microsoft.Extensions.Configuration.IConfigurationBuilder builder) { throw null; }
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationSource.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationSource.cs
index adab1de349a6c..b5a9c68c522db 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationSource.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationSource.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.Extensions.Configuration
 {
     /// <summary>
@@ -11,6 +13,7 @@ public class ChainedConfigurationSource : IConfigurationSource
         /// <summary>
         /// The chained configuration.
         /// </summary>
+        [DisallowNull]
         public IConfiguration? Configuration { get; set; }
 
         /// <summary>

From 48135287366526c05088507923a9a1a3a50d1974 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Fri, 8 Oct 2021 19:06:02 +0300
Subject: [PATCH 14/17] MaybeNullWhen(false)

---
 .../ref/Microsoft.Extensions.Configuration.Abstractions.cs     | 2 +-
 .../src/IConfigurationProvider.cs                              | 3 ++-
 .../ref/Microsoft.Extensions.Configuration.cs                  | 2 +-
 .../src/ConfigurationProvider.cs                               | 3 ++-
 4 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
index a7a7908f1f32e..28bdc674f0b7a 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
@@ -54,7 +54,7 @@ public partial interface IConfigurationProvider
         Microsoft.Extensions.Primitives.IChangeToken GetReloadToken();
         void Load();
         void Set(string key, string? value);
-        bool TryGet(string key, out string? value);
+        bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value);
     }
     public partial interface IConfigurationRoot : Microsoft.Extensions.Configuration.IConfiguration
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
index 20a7e5a6694f8..5bc44411befec 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.Extensions.Configuration
@@ -17,7 +18,7 @@ public interface IConfigurationProvider
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
         /// <returns><c>True</c> if a value for the specified key was found, otherwise <c>false</c>.</returns>
-        bool TryGet(string key, out string? value);
+        bool TryGet(string key, [MaybeNullWhen(false)] out string value);
 
         /// <summary>
         /// Sets a configuration value for the specified key.
diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
index 73e24b774c393..f46fe03a0bbb2 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
@@ -68,7 +68,7 @@ public virtual void Load() { }
         protected void OnReload() { }
         public virtual void Set(string key, string? value) { }
         public override string ToString() { throw null; }
-        public virtual bool TryGet(string key, out string? value) { throw null; }
+        public virtual bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value) { throw null; }
     }
     public partial class ConfigurationReloadToken : Microsoft.Extensions.Primitives.IChangeToken
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
index 9fbeded4fc3de..e3eb4f977bffc 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.Extensions.Primitives;
 
@@ -35,7 +36,7 @@ protected ConfigurationProvider()
         /// <param name="key">The key to lookup.</param>
         /// <param name="value">The value found at key if one is found.</param>
         /// <returns>True if key has a value, false otherwise.</returns>
-        public virtual bool TryGet(string key, out string? value)
+        public virtual bool TryGet(string key, [MaybeNullWhen(false)] out string value)
             => Data.TryGetValue(key, out value);
 
         /// <summary>

From 581c024a9d292fca67a4ebd54788cf1d2ab446ec Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Fri, 8 Oct 2021 19:29:27 +0300
Subject: [PATCH 15/17] Revert "MaybeNullWhen(false)"

This reverts commit 48135287366526c05088507923a9a1a3a50d1974.
---
 .../ref/Microsoft.Extensions.Configuration.Abstractions.cs     | 2 +-
 .../src/IConfigurationProvider.cs                              | 3 +--
 .../ref/Microsoft.Extensions.Configuration.cs                  | 2 +-
 .../src/ConfigurationProvider.cs                               | 3 +--
 4 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
index 28bdc674f0b7a..a7a7908f1f32e 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
@@ -54,7 +54,7 @@ public partial interface IConfigurationProvider
         Microsoft.Extensions.Primitives.IChangeToken GetReloadToken();
         void Load();
         void Set(string key, string? value);
-        bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value);
+        bool TryGet(string key, out string? value);
     }
     public partial interface IConfigurationRoot : Microsoft.Extensions.Configuration.IConfiguration
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
index 5bc44411befec..20a7e5a6694f8 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.Extensions.Configuration
@@ -18,7 +17,7 @@ public interface IConfigurationProvider
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
         /// <returns><c>True</c> if a value for the specified key was found, otherwise <c>false</c>.</returns>
-        bool TryGet(string key, [MaybeNullWhen(false)] out string value);
+        bool TryGet(string key, out string? value);
 
         /// <summary>
         /// Sets a configuration value for the specified key.
diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
index f46fe03a0bbb2..73e24b774c393 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
@@ -68,7 +68,7 @@ public virtual void Load() { }
         protected void OnReload() { }
         public virtual void Set(string key, string? value) { }
         public override string ToString() { throw null; }
-        public virtual bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value) { throw null; }
+        public virtual bool TryGet(string key, out string? value) { throw null; }
     }
     public partial class ConfigurationReloadToken : Microsoft.Extensions.Primitives.IChangeToken
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
index e3eb4f977bffc..9fbeded4fc3de 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationProvider.cs
@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.Extensions.Primitives;
 
@@ -36,7 +35,7 @@ protected ConfigurationProvider()
         /// <param name="key">The key to lookup.</param>
         /// <param name="value">The value found at key if one is found.</param>
         /// <returns>True if key has a value, false otherwise.</returns>
-        public virtual bool TryGet(string key, [MaybeNullWhen(false)] out string value)
+        public virtual bool TryGet(string key, out string? value)
             => Data.TryGetValue(key, out value);
 
         /// <summary>

From ff9af9375a573bd662a151700994c02042076c29 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Mon, 11 Oct 2021 19:12:47 +0300
Subject: [PATCH 16/17] Remove MaybeNullWhen

---
 .../ref/Microsoft.Extensions.Configuration.cs                  | 2 +-
 .../src/ChainedConfigurationProvider.cs                        | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
index 73e24b774c393..3202b47102481 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
@@ -19,7 +19,7 @@ public void Dispose() { }
         public Microsoft.Extensions.Primitives.IChangeToken GetReloadToken() { throw null; }
         public void Load() { }
         public void Set(string key, string? value) { }
-        public bool TryGet(string key, [System.Diagnostics.CodeAnalysis.MaybeNullWhen(false)] out string value) { throw null; }
+        public bool TryGet(string key, out string value) { throw null; }
     }
     public partial class ChainedConfigurationSource : Microsoft.Extensions.Configuration.IConfigurationSource
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
index 53e0660d067e0..c35bb213a8a41 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.Extensions.Configuration
@@ -41,7 +40,7 @@ public ChainedConfigurationProvider(ChainedConfigurationSource source)
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
         /// <returns><c>True</c> if a value for the specified key was found, otherwise <c>false</c>.</returns>
-        public bool TryGet(string key, [MaybeNullWhen(false)] out string value)
+        public bool TryGet(string key, out string value)
         {
             value = _config[key];
             return !string.IsNullOrEmpty(value);

From 3790ba6a2c4076f76a91905563aad6f1568bc920 Mon Sep 17 00:00:00 2001
From: Maksym Koshovyi <maximkoshevoi61@gmail.com>
Date: Mon, 11 Oct 2021 19:19:49 +0300
Subject: [PATCH 17/17] NotNullWhen

---
 .../ref/Microsoft.Extensions.Configuration.cs                   | 2 +-
 .../src/ChainedConfigurationProvider.cs                         | 2 +-
 .../src/ConfigurationManager.cs                                 | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
index 3202b47102481..c9719bcdbbc92 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.cs
@@ -19,7 +19,7 @@ public void Dispose() { }
         public Microsoft.Extensions.Primitives.IChangeToken GetReloadToken() { throw null; }
         public void Load() { }
         public void Set(string key, string? value) { }
-        public bool TryGet(string key, out string value) { throw null; }
+        public bool TryGet(string key, out string? value) { throw null; }
     }
     public partial class ChainedConfigurationSource : Microsoft.Extensions.Configuration.IConfigurationSource
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
index c35bb213a8a41..eb9bed0021145 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ChainedConfigurationProvider.cs
@@ -40,7 +40,7 @@ public ChainedConfigurationProvider(ChainedConfigurationSource source)
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
         /// <returns><c>True</c> if a value for the specified key was found, otherwise <c>false</c>.</returns>
-        public bool TryGet(string key, out string value)
+        public bool TryGet(string key, out string? value)
         {
             value = _config[key];
             return !string.IsNullOrEmpty(value);
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationManager.cs b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationManager.cs
index 377adcfe67b78..6fe4c1a004663 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationManager.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationManager.cs
@@ -339,7 +339,7 @@ public bool Remove(KeyValuePair<string, object> item)
                 return wasRemoved;
             }
 
-            public bool TryGetValue(string key, [MaybeNullWhen(false)] out object value)
+            public bool TryGetValue(string key, [NotNullWhen(true)] out object? value)
             {
                 return _properties.TryGetValue(key, out value);
             }