diff --git a/src/Lucene.Net/Search/FieldCacheImpl.cs b/src/Lucene.Net/Search/FieldCacheImpl.cs
index 93ac26c523..a82214f9e9 100644
--- a/src/Lucene.Net/Search/FieldCacheImpl.cs
+++ b/src/Lucene.Net/Search/FieldCacheImpl.cs
@@ -279,7 +279,7 @@ public virtual void Put(AtomicReader reader, TKey key, TValue value)
 #else
                 lock (readerCache)
                 {
-                    if (!readerCache.TryGetValue(readerKey, out innerCache) || innerCache == null)
+                    if (!readerCache.TryGetValue(readerKey, out innerCache) || innerCache is null)
                     {
                         // First time this reader is using FieldCache
                         innerCache = new ConcurrentDictionary<TKey, object>
@@ -313,7 +313,7 @@ public virtual TValue Get(AtomicReader reader, TKey key, bool setDocsWithField)
 #else
                 lock (readerCache)
                 {
-                    if (!readerCache.TryGetValue(readerKey, out innerCache) || innerCache == null)
+                    if (!readerCache.TryGetValue(readerKey, out innerCache) || innerCache is null)
                     {
                         // First time this reader is using FieldCache
                         innerCache = new ConcurrentDictionary<TKey, object>
@@ -357,7 +357,7 @@ public virtual TValue Get(AtomicReader reader, TKey key, bool setDocsWithField)
                 return (TValue)value;
             }
 
-            private void PrintNewInsanity(TextWriter infoStream, object value)
+            private void PrintNewInsanity(TextWriter infoStream, TValue value)
             {
                 FieldCacheSanityChecker.Insanity[] insanities = FieldCacheSanityChecker.CheckSanity(wrapper);
                 for (int i = 0; i < insanities.Length; i++)
@@ -366,7 +366,7 @@ private void PrintNewInsanity(TextWriter infoStream, object value)
                     FieldCache.CacheEntry[] entries = insanity.CacheEntries;
                     for (int j = 0; j < entries.Length; j++)
                     {
-                        if (entries[j].Value == value)
+                        if (ReferenceEquals(entries[j].Value, value))
                         {
                             // OK this insanity involves our entry
                             infoStream.WriteLine("WARNING: new FieldCache insanity created\nDetails: " + insanity.ToString());
@@ -476,7 +476,7 @@ public override bool Equals(object o)
             /// Composes a hashcode based on the field and type. </summary>
             public override int GetHashCode()
             {
-                return field.GetHashCode() ^ (custom == null ? 0 : custom.GetHashCode());
+                return field.GetHashCode() ^ (custom is null ? 0 : custom.GetHashCode());
             }
         }
 
@@ -520,7 +520,7 @@ public virtual void DoUninvert(AtomicReader reader, string field, bool setDocsWi
                             VisitDoc(docID);
                             if (setDocsWithField)
                             {
-                                if (docsWithField == null)
+                                if (docsWithField is null)
                                 {
                                     // Lazy init
                                     this.docsWithField = docsWithField = new FixedBitSet(maxDoc);
@@ -544,11 +544,13 @@ internal virtual void SetDocsWithField(AtomicReader reader, string field, IBits
         {
             int maxDoc = reader.MaxDoc;
             IBits bits;
-            if (docsWithField == null)
+            if (docsWithField is null)
             {
                 bits = new Lucene.Net.Util.Bits.MatchNoBits(maxDoc);
             }
+#pragma warning disable IDE0038 // Use pattern matching
             else if (docsWithField is FixedBitSet)
+#pragma warning restore IDE0038 // Use pattern matching
             {
                 int numSet = ((FixedBitSet)docsWithField).Cardinality();
                 if (numSet >= maxDoc)
@@ -601,7 +603,7 @@ public virtual FieldCache.Bytes GetBytes(AtomicReader reader, string field, Fiel
             else
             {
                 FieldInfo info = reader.FieldInfos.FieldInfo(field);
-                if (info == null)
+                if (info is null)
                 {
                     return FieldCache.Bytes.EMPTY;
                 }
@@ -653,7 +655,7 @@ protected override FieldCache.Bytes CreateValue(AtomicReader reader, CacheKey<Fi
 #pragma warning disable 612, 618
                 FieldCache.IByteParser parser = key.custom;
 #pragma warning restore 612, 618
-                if (parser == null)
+                if (parser is null)
                 {
                     // Confusing: must delegate to wrapper (vs simply
                     // setting parser = DEFAULT_INT16_PARSER) so cache
@@ -759,7 +761,7 @@ public virtual FieldCache.Int16s GetInt16s(AtomicReader reader, string field, Fi
             else
             {
                 FieldInfo info = reader.FieldInfos.FieldInfo(field);
-                if (info == null)
+                if (info is null)
                 {
                     return FieldCache.Int16s.EMPTY;
                 }
@@ -814,7 +816,7 @@ protected override FieldCache.Int16s CreateValue(AtomicReader reader, CacheKey<F
                 short[] values;
 #pragma warning disable 612, 618
                 FieldCache.IInt16Parser parser = key.custom;
-                if (parser == null)
+                if (parser is null)
                 {
                     // Confusing: must delegate to wrapper (vs simply
                     // setting parser = DEFAULT_INT16_PARSER) so cache
@@ -916,7 +918,7 @@ public virtual FieldCache.Int32s GetInt32s(AtomicReader reader, string field, Fi
             else
             {
                 FieldInfo info = reader.FieldInfos.FieldInfo(field);
-                if (info == null)
+                if (info is null)
                 {
                     return FieldCache.Int32s.EMPTY;
                 }
@@ -995,7 +997,7 @@ internal Int32Cache(FieldCacheImpl wrapper)
             protected override FieldCache.Int32s CreateValue(AtomicReader reader, CacheKey<FieldCache.IInt32Parser> key, bool setDocsWithField)
             {
                 FieldCache.IInt32Parser parser = key.custom;
-                if (parser == null)
+                if (parser is null)
                 {
                     // Confusing: must delegate to wrapper (vs simply
                     // setting parser =
@@ -1025,7 +1027,7 @@ protected override FieldCache.Int32s CreateValue(AtomicReader reader, CacheKey<F
                     wrapper.SetDocsWithField(reader, key.field, u.docsWithField);
                 }
                 GrowableWriterAndMinValue values = valuesRef.Get();
-                if (values == null)
+                if (values is null)
                 {
                     return new Int32sFromArray(new PackedInt32s.NullReader(reader.MaxDoc), 0);
                 }
@@ -1052,7 +1054,7 @@ public UninvertAnonymousInnerClassHelper(AtomicReader reader, FieldCache.IInt32P
                 protected override void VisitTerm(BytesRef term)
                 {
                     currentValue = parser.ParseInt32(term);
-                    if (values == null)
+                    if (values is null)
                     {
                         // Lazy alloc so for the numeric field case
                         // (which will hit a FormatException
@@ -1094,7 +1096,7 @@ protected override TermsEnum GetTermsEnum(Terms terms)
         public virtual IBits GetDocsWithField(AtomicReader reader, string field)
         {
             FieldInfo fieldInfo = reader.FieldInfos.FieldInfo(field);
-            if (fieldInfo == null)
+            if (fieldInfo is null)
             {
                 // field does not exist or has no value
                 return new Lucene.Net.Util.Bits.MatchNoBits(reader.MaxDoc);
@@ -1139,7 +1141,7 @@ protected override IBits CreateValue(AtomicReader reader, CacheKey key, bool set
                     DocsEnum docs = null;
                     while (termsEnum.MoveNext())
                     {
-                        if (res == null)
+                        if (res is null)
                         {
                             // lazy init
                             res = new FixedBitSet(maxDoc);
@@ -1158,7 +1160,7 @@ protected override IBits CreateValue(AtomicReader reader, CacheKey key, bool set
                         }
                     }
                 }
-                if (res == null)
+                if (res is null)
                 {
                     return new Lucene.Net.Util.Bits.MatchNoBits(maxDoc);
                 }
@@ -1196,7 +1198,7 @@ public virtual FieldCache.Singles GetSingles(AtomicReader reader, string field,
             else
             {
                 FieldInfo info = reader.FieldInfos.FieldInfo(field);
-                if (info == null)
+                if (info is null)
                 {
                     return FieldCache.Singles.EMPTY;
                 }
@@ -1244,7 +1246,7 @@ internal SingleCache(FieldCacheImpl wrapper)
             protected override FieldCache.Singles CreateValue(AtomicReader reader, CacheKey<FieldCache.ISingleParser> key, bool setDocsWithField)
             {
                 FieldCache.ISingleParser parser = key.custom;
-                if (parser == null)
+                if (parser is null)
                 {
                     // Confusing: must delegate to wrapper (vs simply
                     // setting parser =
@@ -1275,7 +1277,7 @@ protected override FieldCache.Singles CreateValue(AtomicReader reader, CacheKey<
                 }
 
                 float[] values = valuesRef.Get();
-                if (values == null)
+                if (values is null)
                 {
                     values = new float[reader.MaxDoc];
                 }
@@ -1301,7 +1303,7 @@ public UninvertAnonymousInnerClassHelper(AtomicReader reader, FieldCache.ISingle
                 protected override void VisitTerm(BytesRef term)
                 {
                     currentValue = parser.ParseSingle(term);
-                    if (values == null)
+                    if (values is null)
                     {
                         // Lazy alloc so for the numeric field case
                         // (which will hit a FormatException
@@ -1347,7 +1349,7 @@ public virtual FieldCache.Int64s GetInt64s(AtomicReader reader, string field, Fi
             else
             {
                 FieldInfo info = reader.FieldInfos.FieldInfo(field);
-                if (info == null)
+                if (info is null)
                 {
                     return FieldCache.Int64s.EMPTY;
                 }
@@ -1397,7 +1399,7 @@ internal Int64Cache(FieldCacheImpl wrapper)
             protected override FieldCache.Int64s CreateValue(AtomicReader reader, CacheKey<FieldCache.IInt64Parser> key, bool setDocsWithField)
             {
                 FieldCache.IInt64Parser parser = key.custom;
-                if (parser == null)
+                if (parser is null)
                 {
                     // Confusing: must delegate to wrapper (vs simply
                     // setting parser =
@@ -1427,7 +1429,7 @@ protected override FieldCache.Int64s CreateValue(AtomicReader reader, CacheKey<F
                     wrapper.SetDocsWithField(reader, key.field, u.docsWithField);
                 }
                 GrowableWriterAndMinValue values = valuesRef.Get();
-                if (values == null)
+                if (values is null)
                 {
                     return new Int64sFromArray(new PackedInt32s.NullReader(reader.MaxDoc), 0L);
                 }
@@ -1454,7 +1456,7 @@ public UninvertAnonymousInnerClassHelper(AtomicReader reader, FieldCache.IInt64P
                 protected override void VisitTerm(BytesRef term)
                 {
                     currentValue = parser.ParseInt64(term);
-                    if (values == null)
+                    if (values is null)
                     {
                         // Lazy alloc so for the numeric field case
                         // (which will hit a FormatException
@@ -1510,7 +1512,7 @@ public virtual FieldCache.Doubles GetDoubles(AtomicReader reader, string field,
             else
             {
                 FieldInfo info = reader.FieldInfos.FieldInfo(field);
-                if (info == null)
+                if (info is null)
                 {
                     return FieldCache.Doubles.EMPTY;
                 }
@@ -1552,7 +1554,7 @@ internal DoubleCache(FieldCacheImpl wrapper)
             protected override FieldCache.Doubles CreateValue(AtomicReader reader, CacheKey<FieldCache.IDoubleParser> key, bool setDocsWithField)
             {
                 FieldCache.IDoubleParser parser = key.custom;
-                if (parser == null)
+                if (parser is null)
                 {
                     // Confusing: must delegate to wrapper (vs simply
                     // setting parser =
@@ -1582,7 +1584,7 @@ protected override FieldCache.Doubles CreateValue(AtomicReader reader, CacheKey<
                     wrapper.SetDocsWithField(reader, key.field, u.docsWithField);
                 }
                 double[] values = valuesRef.Get();
-                if (values == null)
+                if (values is null)
                 {
                     values = new double[reader.MaxDoc];
                 }
@@ -1608,7 +1610,7 @@ public UninvertAnonymousInnerClassHelper(AtomicReader reader, FieldCache.IDouble
                 protected override void VisitTerm(BytesRef term)
                 {
                     currentValue = parser.ParseDouble(term);
-                    if (values == null)
+                    if (values is null)
                     {
                         // Lazy alloc so for the numeric field case
                         // (which will hit a FormatException
@@ -1683,7 +1685,7 @@ public virtual SortedDocValues GetTermsIndex(AtomicReader reader, string field,
             else
             {
                 FieldInfo info = reader.FieldInfos.FieldInfo(field);
-                if (info == null)
+                if (info is null)
                 {
                     return DocValues.EMPTY_SORTED;
                 }
@@ -1838,7 +1840,7 @@ public virtual BinaryDocValues GetTerms(AtomicReader reader, string field, bool
         public virtual BinaryDocValues GetTerms(AtomicReader reader, string field, bool setDocsWithField, float acceptableOverheadRatio)
         {
             BinaryDocValues valuesIn = reader.GetBinaryDocValues(field);
-            if (valuesIn == null)
+            if (valuesIn is null)
             {
                 valuesIn = reader.GetSortedDocValues(field);
             }
@@ -1851,7 +1853,7 @@ public virtual BinaryDocValues GetTerms(AtomicReader reader, string field, bool
             }
 
             FieldInfo info = reader.FieldInfos.FieldInfo(field);
-            if (info == null)
+            if (info is null)
             {
                 return DocValues.EMPTY_BINARY;
             }
@@ -2001,7 +2003,7 @@ public virtual SortedSetDocValues GetDocTermOrds(AtomicReader reader, string fie
             }
 
             FieldInfo info = reader.FieldInfos.FieldInfo(field);
-            if (info == null)
+            if (info is null)
             {
                 return DocValues.EMPTY_SORTED_SET;
             }
@@ -2040,7 +2042,7 @@ public virtual TextWriter InfoStream
             set =>
                 // LUCENENET specific - use a SafeTextWriterWrapper to ensure that if the TextWriter
                 // is disposed by the caller (using block) we don't get any exceptions if we keep using it.
-                infoStream = value == null
+                infoStream = value is null
                     ? null
                     : (value is SafeTextWriterWrapper ? value : new SafeTextWriterWrapper(value));
         }