BUG: Lucene.Net.Search.FieldComparer.TermValComparer: Using a singlet…

…on instance breaks missing vs empty field comparison because the static fields MISSING_BYTES and NON_MISSING_BYTES are tested for reference equality.

src/Lucene.Net/Search/FieldComparator.cs

@@ -1452,10 +1452,14 @@ public override int CompareValues(BytesRef val1, BytesRef val2)
         // TODO: should we remove this?  who really uses it?
         public sealed class TermValComparer : FieldComparer<BytesRef>
         {
+            // LUCENENET NOTE: We can't use Arrays.Empty<byte>() here because
+            // MISSING_BYTES and NON_MISSING_BYTES are compared for reference
+            // equality and Arrays.Empty<byte>() returns a singleton instance.
+
             // sentinels, just used internally in this comparer
-            private static readonly byte[] MISSING_BYTES = Arrays.Empty<byte>();
+            private static readonly byte[] MISSING_BYTES = new byte[0];
 
-            private static readonly byte[] NON_MISSING_BYTES = Arrays.Empty<byte>();
+            private static readonly byte[] NON_MISSING_BYTES = new byte[0];
 
             private readonly BytesRef[] values; // LUCENENET: marked readonly
             private BinaryDocValues docTerms;
@@ -1577,4 +1581,4 @@ private void SetMissingBytes(int doc, BytesRef br)
             }
         }
     }
-}
+}