Initialize list arguments with non-null values

src/Microsoft.DotNet.XHarness.CLI/CommandArguments/Apple/Arguments/MlaunchArgument.cs

@@ -15,9 +15,8 @@ namespace Microsoft.DotNet.XHarness.CLI.CommandArguments.Apple
     /// </summary>
     internal class MlaunchArgument : Argument<string>
     {
-        public MlaunchArgument() : base("mlaunch=", "Path to the mlaunch binary")
+        public MlaunchArgument() : base("mlaunch=", "Path to the mlaunch binary", MacOSProcessManager.DetectMlaunchPath())
         {
-            Value = MacOSProcessManager.DetectMlaunchPath();
         }
 
         public override void Action(string argumentValue) => Value = RootPath(argumentValue);

src/Microsoft.DotNet.XHarness.CLI/CommandArguments/Apple/Arguments/TargetArgument.cs

@@ -13,9 +13,8 @@ namespace Microsoft.DotNet.XHarness.CLI.CommandArguments.Apple
     /// </summary>
     internal class TargetArgument : Argument<TestTargetOs>
     {
-        public TargetArgument() : base("target=|targets=|t=", "Test target (device/simulator and OS)")
+        public TargetArgument() : base("target=|targets=|t=", "Test target (device/simulator and OS)", TestTargetOs.None)
         {
-            Value = TestTargetOs.None;
         }
 
         public override void Action(string argumentValue)

src/Microsoft.DotNet.XHarness.CLI/CommandArguments/Argument.cs

@@ -124,7 +124,7 @@ public abstract class Argument<T> : Argument
     {
         public virtual T Value { get; protected set; }
 
-        protected Argument(string prototype, string description, T defaultValue = default!)
+        protected Argument(string prototype, string description, T defaultValue)
             : base(prototype, description)
         {
             Value = defaultValue;
@@ -138,9 +138,8 @@ protected Argument(string prototype, string description, T defaultValue = defaul
     public abstract class IntArgument : Argument<int>
     {
         public IntArgument(string prototype, string description, int defaultValue = 0)
-            : base(prototype, description)
+            : base(prototype, description, defaultValue)
         {
-            Value = defaultValue;
         }
 
         public override void Action(string argumentValue)
@@ -158,7 +157,7 @@ public override void Action(string argumentValue)
     public abstract class StringArgument : Argument<string?>
     {
         public StringArgument(string prototype, string description)
-            : base(prototype, description)
+            : base(prototype, description, null)
         {
         }
 
@@ -186,9 +185,8 @@ public override void Validate()
     public abstract class TimeSpanArgument : Argument<TimeSpan>
     {
         protected TimeSpanArgument(string prototype, string description, TimeSpan defaultValue)
-            : base(prototype, description)
+            : base(prototype, description, defaultValue)
         {
-            Value = defaultValue;
         }
 
         public override void Action(string argumentValue)
@@ -243,9 +241,8 @@ public abstract class SwitchArgument : Argument<bool>
         private readonly bool _defaultValue;
 
         public SwitchArgument(string prototype, string description, bool defaultValue)
-            : base(prototype, description)
+            : base(prototype, description, defaultValue)
         {
-            Value = defaultValue;
             _defaultValue = defaultValue;
         }
 
@@ -271,7 +268,7 @@ public abstract class RepeatableArgument : Argument<IEnumerable<string>>
     {
         private readonly List<string> _values = new();
 
-        protected RepeatableArgument(string prototype, string description) : base(prototype, description + ". Can be used more than once")
+        protected RepeatableArgument(string prototype, string description) : base(prototype, description + ". Can be used more than once", Array.Empty<string>())
         {
         }
 

src/Microsoft.DotNet.XHarness.CLI/CommandArguments/Arguments/WebServerHttpEnvironmentVariables.cs

@@ -2,14 +2,18 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 
 namespace Microsoft.DotNet.XHarness.CLI.CommandArguments
 {
     internal class WebServerHttpEnvironmentVariables : Argument<IEnumerable<string>>
     {
         public WebServerHttpEnvironmentVariables()
-            : base("set-web-server-http-env=", "Comma separated list of environment variable names, which should be set to HTTP host and port, for the unit test, which use xharness as test web server")
+            : base(
+                  "set-web-server-http-env=",
+                  "Comma separated list of environment variable names, which should be set to HTTP host and port, for the unit test, which use xharness as test web server",
+                  Array.Empty<string>())
         {
         }
 

src/Microsoft.DotNet.XHarness.CLI/CommandArguments/Arguments/WebServerHttpsEnvironmentVariables.cs

@@ -2,14 +2,18 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 
 namespace Microsoft.DotNet.XHarness.CLI.CommandArguments
 {
     internal class WebServerHttpsEnvironmentVariables : Argument<IEnumerable<string>>
     {
         public WebServerHttpsEnvironmentVariables()
-            : base("set-web-server-https-env=", "Comma separated list of environment variable names, which should be set to HTTPS host and port, for the unit test, which use xharness as test web server")
+            : base(
+                  "set-web-server-https-env=",
+                  "Comma separated list of environment variable names, which should be set to HTTPS host and port, for the unit test, which use xharness as test web server",
+                  Array.Empty<string>())
         {
         }
 

src/Microsoft.DotNet.XHarness.CLI/CommandArguments/Arguments/WebServerMiddlewareArgument.cs

@@ -11,7 +11,10 @@ namespace Microsoft.DotNet.XHarness.CLI.CommandArguments
     internal class WebServerMiddlewareArgument : Argument<List<(string path, string type)>>
     {
         public WebServerMiddlewareArgument()
-            : base("web-server-middleware=", "<path>,<typeName> to assembly and type which contains Kestrel middleware for local test server. Could be used multiple times to load multiple middlewares", new List<(string path, string type)>())
+            : base(
+                  "web-server-middleware=",
+                  "<path>,<typeName> to assembly and type which contains Kestrel middleware for local test server. Could be used multiple times to load multiple middlewares",
+                  new List<(string path, string type)>())
         {
         }