Replace int.MinValue with MergeTrigger.NONE

The original Java code uses null, but that causes problems if you make
the enum nullable. This is a cleaner solution although it is an API
mismatch from the Java semantics.

src/Lucene.Net.TestFramework/Index/MockRandomMergePolicy.cs

@@ -116,8 +116,8 @@ public override MergeSpecification FindForcedMerges(SegmentInfos segmentInfos, i
 
         public override MergeSpecification FindForcedDeletesMerges(SegmentInfos segmentInfos)
         {
-            // LUCENENET specific - just use int.MinValue to indicate "null"
-            return FindMerges((MergeTrigger)int.MinValue, segmentInfos);
+            // LUCENENET specific - use NONE instead of null
+            return FindMerges(MergeTrigger.NONE, segmentInfos);
         }
 
         protected override void Dispose(bool disposing)
@@ -130,4 +130,4 @@ public override bool UseCompoundFile(SegmentInfos infos, SegmentCommitInfo merge
             return random.Next(5) != 1;
         }
     }
-}
+}

src/Lucene.Net.Tests/Index/TestNoMergePolicy.cs

@@ -32,7 +32,7 @@ public class TestNoMergePolicy : LuceneTestCase
         public virtual void TestNoMergePolicy_Mem()
         {
             MergePolicy mp = NoMergePolicy.NO_COMPOUND_FILES;
-            Assert.IsNull(mp.FindMerges(/*null*/ (MergeTrigger)int.MinValue, (SegmentInfos)null));
+            Assert.IsNull(mp.FindMerges(/*null*/ MergeTrigger.NONE, (SegmentInfos)null));
             Assert.IsNull(mp.FindForcedMerges(null, 0, null));
             Assert.IsNull(mp.FindForcedDeletesMerges(null));
             Assert.IsFalse(mp.UseCompoundFile(null, null));
@@ -82,4 +82,4 @@ public virtual void TestMethodsOverridden()
             }
         }
     }
-}
+}

src/Lucene.Net/Index/MergeTrigger.cs

@@ -24,6 +24,11 @@ namespace Lucene.Net.Index
     /// </summary>
     public enum MergeTrigger
     {
+        /// <summary>
+        /// LUCENENET-specific value to be used instead of null.
+        /// </summary>
+        NONE = -1,
+
         /// <summary>
         /// Merge was triggered by a segment flush.
         /// </summary>
@@ -50,4 +55,4 @@ public enum MergeTrigger
         /// </summary>
         CLOSING
     }
-}
+}

src/Lucene.Net/Index/UpgradeIndexMergePolicy.cs

@@ -83,8 +83,8 @@ public override void SetIndexWriter(IndexWriter writer)
 
         public override MergeSpecification FindMerges(MergeTrigger mergeTrigger, SegmentInfos segmentInfos)
         {
-            // LUCENENET specific - just use min value to indicate "null" for merge trigger
-            return m_base.FindMerges((MergeTrigger)int.MinValue, segmentInfos);
+            // LUCENENET specific - use NONE instead of null
+            return m_base.FindMerges(MergeTrigger.NONE, segmentInfos);
         }
 
         public override MergeSpecification FindForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount, IDictionary<SegmentCommitInfo, bool> segmentsToMerge)
@@ -163,7 +163,7 @@ public override bool UseCompoundFile(SegmentInfos segments, SegmentCommitInfo ne
         protected override void Dispose(bool disposing)
         {
             if (disposing)
-            { 
+            {
                 m_base.Dispose();
             }
         }
@@ -184,4 +184,4 @@ private void Message(string message)
             m_writer.Get().infoStream.Message("UPGMP", message);
         }
     }
-}
+}