Update Corelib to adapt to compiler nullability updates

38 files changed, 97 insertions, 107 deletions

diff --git a/src/System.Private.CoreLib/shared/Internal/Win32/RegistryKey.cs b/src/System.Private.CoreLib/shared/Internal/Win32/RegistryKey.cs
index 6f4c31255c..cec8e2f32d 100644
--- a/src/System.Private.CoreLib/shared/Internal/Win32/RegistryKey.cs
+++ b/src/System.Private.CoreLib/shared/Internal/Win32/RegistryKey.cs
@@ -371,7 +371,7 @@ namespace Internal.Win32
                         // make sure the string is null terminated before processing the data
                         if (blob.Length > 0 && blob[blob.Length - 1] != (char)0)
                         {
-                            Array.Resize(ref blob!, blob.Length + 1); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                            Array.Resize(ref blob, blob.Length + 1);
                         }
 
                         string[] strings = Array.Empty<string>();
@@ -416,13 +416,13 @@ namespace Internal.Win32
                             {
                                 if (strings.Length == stringsCount)
                                 {
-                                    Array.Resize(ref strings!, stringsCount > 0 ? stringsCount * 2 : 4); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                                    Array.Resize(ref strings, stringsCount > 0 ? stringsCount * 2 : 4);
                                 }
                                 strings[stringsCount++] = toAdd;
                             }
                         }
 
-                        Array.Resize(ref strings!, stringsCount); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                        Array.Resize(ref strings, stringsCount);
                         data = strings;
                     }
                     break;
diff --git a/src/System.Private.CoreLib/shared/Interop/Unix/System.Native/Interop.MountPoints.cs b/src/System.Private.CoreLib/shared/Interop/Unix/System.Native/Interop.MountPoints.cs
index a2fe2078b6..134dcb9203 100644
--- a/src/System.Private.CoreLib/shared/Interop/Unix/System.Native/Interop.MountPoints.cs
+++ b/src/System.Private.CoreLib/shared/Interop/Unix/System.Native/Interop.MountPoints.cs
@@ -27,13 +27,13 @@ internal static partial class Interop
                 {
                     if (count == found.Length)
                     {
-                        Array.Resize(ref found!, count * 2); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                        Array.Resize(ref found, count * 2);
                     }
                     found[count++] = Marshal.PtrToStringAnsi((IntPtr)name)!;
                 });
             }
 
-            Array.Resize(ref found!, count); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            Array.Resize(ref found, count);
             return found;
         }
     }
diff --git a/src/System.Private.CoreLib/shared/System/Collections/Generic/Dictionary.cs b/src/System.Private.CoreLib/shared/System/Collections/Generic/Dictionary.cs
index fbd6ac7cee..fc4d875289 100644
--- a/src/System.Private.CoreLib/shared/System/Collections/Generic/Dictionary.cs
+++ b/src/System.Private.CoreLib/shared/System/Collections/Generic/Dictionary.cs
@@ -675,7 +675,7 @@ namespace System.Collections.Generic
 
         public virtual void OnDeserialization(object? sender)
         {
-            HashHelpers.SerializationInfoTable.TryGetValue(this, out SerializationInfo siInfo);
+            HashHelpers.SerializationInfoTable.TryGetValue(this, out SerializationInfo? siInfo);
 
             if (siInfo == null)
             {
diff --git a/src/System.Private.CoreLib/shared/System/Collections/Hashtable.cs b/src/System.Private.CoreLib/shared/System/Collections/Hashtable.cs
index f5a90e654e..b74de8225b 100644
--- a/src/System.Private.CoreLib/shared/System/Collections/Hashtable.cs
+++ b/src/System.Private.CoreLib/shared/System/Collections/Hashtable.cs
@@ -1161,7 +1161,7 @@ namespace System.Collections
                 return;
             }
 
-            SerializationInfo siInfo;
+            SerializationInfo? siInfo;
             HashHelpers.SerializationInfoTable.TryGetValue(this, out siInfo);
 
             if (siInfo == null)
diff --git a/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/CounterGroup.cs b/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/CounterGroup.cs
index d669114d50..0879f9d9f4 100644
--- a/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/CounterGroup.cs
+++ b/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/CounterGroup.cs
@@ -52,11 +52,9 @@ namespace System.Diagnostics.Tracing
         {
             if (e.Command == EventCommand.Enable || e.Command == EventCommand.Update)
             {
-                string valueStr;
-                float value;
                 Debug.Assert(e.Arguments != null);
 
-                if (e.Arguments.TryGetValue("EventCounterIntervalSec", out valueStr) && float.TryParse(valueStr, out value))
+                if (e.Arguments.TryGetValue("EventCounterIntervalSec", out string? valueStr) && float.TryParse(valueStr, out float value))
                 {
                     lock (this)      // Lock the CounterGroup
                     {
diff --git a/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs b/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs
index a914b930a1..d06e292e8f 100644
--- a/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs
+++ b/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs
@@ -1734,7 +1734,7 @@ namespace System.Diagnostics.Tracing
             hash.Start();
             hash.Append(namespaceBytes);
             hash.Append(bytes);
-            Array.Resize(ref bytes!, 16); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            Array.Resize(ref bytes, 16);
             hash.Finish(bytes);
 
             bytes[7] = unchecked((byte)((bytes[7] & 0x0F) | 0x50));    // Set high 4 bits of octet 7 to 5, as per RFC 4122
@@ -5446,8 +5446,8 @@ namespace System.Diagnostics.Tracing
                 {
                     ManifestError(SR.Format(SR.EventSource_IllegalOpcodeValue, name, value));
                 }
-                string prevName;
-                if (opcodeTab.TryGetValue(value, out prevName) && !name.Equals(prevName, StringComparison.Ordinal))
+
+                if (opcodeTab.TryGetValue(value, out string? prevName) && !name.Equals(prevName, StringComparison.Ordinal))
                 {
                     ManifestError(SR.Format(SR.EventSource_OpcodeCollision, name, prevName, value));
                 }
@@ -5462,8 +5462,8 @@ namespace System.Diagnostics.Tracing
                 {
                     ManifestError(SR.Format(SR.EventSource_IllegalTaskValue, name, value));
                 }
-                string prevName;
-                if (taskTab != null && taskTab.TryGetValue(value, out prevName) && !name.Equals(prevName, StringComparison.Ordinal))
+
+                if (taskTab != null && taskTab.TryGetValue(value, out string? prevName) && !name.Equals(prevName, StringComparison.Ordinal))
                 {
                     ManifestError(SR.Format(SR.EventSource_TaskCollision, name, prevName, value));
                 }
@@ -5484,8 +5484,8 @@ namespace System.Diagnostics.Tracing
                 {
                     ManifestError(SR.Format(SR.EventSource_IllegalKeywordsValue, name, "0x" + value.ToString("x", CultureInfo.CurrentCulture)));
                 }
-                string prevName;
-                if (keywordTab != null && keywordTab.TryGetValue(value, out prevName) && !name.Equals(prevName, StringComparison.Ordinal))
+
+                if (keywordTab != null && keywordTab.TryGetValue(value, out string? prevName) && !name.Equals(prevName, StringComparison.Ordinal))
                 {
                     ManifestError(SR.Format(SR.EventSource_KeywordCollision, name, prevName, "0x" + value.ToString("x", CultureInfo.CurrentCulture)));
                 }
@@ -5652,10 +5652,9 @@ namespace System.Diagnostics.Tracing
 
             // at this point we have all the information we need to translate the C# Message
             // to the manifest string we'll put in the stringTab
-            string msg;
-            if (stringTab.TryGetValue("event_" + eventName, out msg))
+            if (stringTab.TryGetValue("event_" + eventName, out string? msg))
             {
-                msg = TranslateToManifestConvention(msg!, eventName); // https://github.com/dotnet/roslyn/issues/26761
+                msg = TranslateToManifestConvention(msg, eventName);
                 stringTab["event_" + eventName] = msg;
             }
 
@@ -5687,7 +5686,7 @@ namespace System.Diagnostics.Tracing
             if (channelTab.Count == MaxCountChannels)
                 ManifestError(SR.EventSource_MaxChannelExceeded);
 
-            ChannelInfo info;
+            ChannelInfo? info;
             if (!channelTab.TryGetValue((int)channel, out info))
             {
                 // If we were not given an explicit channel, allocate one.  
@@ -5967,8 +5966,8 @@ namespace System.Diagnostics.Tracing
                 return;
 
             stringBuilder.Append(" message=\"$(string.").Append(key).Append(")\"");
-            string prevValue;
-            if (stringTab.TryGetValue(key, out prevValue) && !prevValue.Equals(value))
+
+            if (stringTab.TryGetValue(key, out string? prevValue) && !prevValue.Equals(value))
             {
                 ManifestError(SR.Format(SR.EventSource_DuplicateStringKey, key), true);
                 return;
@@ -6045,7 +6044,7 @@ namespace System.Diagnostics.Tracing
             if (resources != null && eventMessage == null)
                 eventMessage = resources.GetString("event_" + eventName, CultureInfo.InvariantCulture);
 
-            Debug.Assert(info.Attribs != null);
+            Debug.Assert(info!.Attribs != null);
             if (info.Attribs.EventChannelType == EventChannelType.Admin && eventMessage == null)
                 ManifestError(SR.Format(SR.EventSource_EventWithAdminChannelMustHaveMessage, eventName, info.Name));
             return info.Name;
@@ -6056,7 +6055,7 @@ namespace System.Diagnostics.Tracing
             if (task == EventTask.None)
                 return "";
 
-            string ret;
+            string? ret;
             if (taskTab == null)
                 taskTab = new Dictionary<int, string>();
             if (!taskTab.TryGetValue((int)task, out ret))
@@ -6209,14 +6208,14 @@ namespace System.Diagnostics.Tracing
                     if (stringBuilder == null)
                         return eventMessage;
                     UpdateStringBuilder(ref stringBuilder, eventMessage, writtenSoFar, i - writtenSoFar);
-                    return stringBuilder!.ToString(); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                    return stringBuilder.ToString();
                 }
 
                 if (eventMessage[i] == '%')
                 {
                     // handle format message escaping character '%' by escaping it
                     UpdateStringBuilder(ref stringBuilder, eventMessage, writtenSoFar, i - writtenSoFar);
-                    stringBuilder!.Append("%%"); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                    stringBuilder.Append("%%");
                     i++;
                     writtenSoFar = i;
                 }
@@ -6225,7 +6224,7 @@ namespace System.Diagnostics.Tracing
                 {
                     // handle C# escaped '{" and '}'
                     UpdateStringBuilder(ref stringBuilder, eventMessage, writtenSoFar, i - writtenSoFar);
-                    stringBuilder!.Append(eventMessage[i]); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                    stringBuilder.Append(eventMessage[i]);
                     i++; i++;
                     writtenSoFar = i;
                 }
@@ -6244,7 +6243,7 @@ namespace System.Diagnostics.Tracing
                         i++;
                         UpdateStringBuilder(ref stringBuilder, eventMessage, writtenSoFar, leftBracket - writtenSoFar);
                         int manIndex = TranslateIndexToManifestConvention(argNum, evtName);
-                        stringBuilder!.Append('%').Append(manIndex); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                        stringBuilder.Append('%').Append(manIndex);
                         // An '!' after the insert specifier {n} will be interpreted as a literal.
                         // We'll escape it so that mc.exe does not attempt to consider it the 
                         // beginning of a format string.
@@ -6264,7 +6263,7 @@ namespace System.Diagnostics.Tracing
                 {
                     UpdateStringBuilder(ref stringBuilder, eventMessage, writtenSoFar, i - writtenSoFar);
                     i++;
-                    stringBuilder!.Append(s_escapes[chIdx]); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                    stringBuilder.Append(s_escapes[chIdx]);
                     writtenSoFar = i;
                 }
                 else
@@ -6274,7 +6273,7 @@ namespace System.Diagnostics.Tracing
 
         private int TranslateIndexToManifestConvention(int idx, string evtName)
         {
-            List<int> byteArrArgIndices;
+            List<int>? byteArrArgIndices;
             if (perEventByteArrayArgIndices.TryGetValue(evtName, out byteArrArgIndices))
             {
                 foreach (var byArrIdx in byteArrArgIndices)
diff --git a/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/TraceLogging/TraceLoggingTypeInfo.cs b/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/TraceLogging/TraceLoggingTypeInfo.cs
index f31765c2f3..45d4f77caa 100644
--- a/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/TraceLogging/TraceLoggingTypeInfo.cs
+++ b/src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/TraceLogging/TraceLoggingTypeInfo.cs
@@ -189,7 +189,7 @@ namespace System.Diagnostics.Tracing
         {
             var cache = threadCache ?? (threadCache = new Dictionary<Type, TraceLoggingTypeInfo>());
 
-            TraceLoggingTypeInfo instance;
+            TraceLoggingTypeInfo? instance;
             if (!cache.TryGetValue(type, out instance))
             {
                 if (recursionCheck == null)
diff --git a/src/System.Private.CoreLib/shared/System/Environment.Unix.cs b/src/System.Private.CoreLib/shared/System/Environment.Unix.cs
index 0d802dcec9..9a2af4dfb8 100644
--- a/src/System.Private.CoreLib/shared/System/Environment.Unix.cs
+++ b/src/System.Private.CoreLib/shared/System/Environment.Unix.cs
@@ -75,16 +75,14 @@ namespace System
             {
                 Debug.Assert(option == SpecialFolderOption.Create);
 
-#pragma warning disable CS8634 // TODO-NULLABLE: Remove warning disable when nullable attributes are respected
                 // TODO #11151: Replace with Directory.CreateDirectory once we have access to System.IO.FileSystem here.
                 Func<string, object> createDirectory = LazyInitializer.EnsureInitialized(ref s_directoryCreateDirectory, () =>
                 {
                     Type dirType = Type.GetType("System.IO.Directory, System.IO.FileSystem, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", throwOnError: true)!;
                     MethodInfo mi = dirType.GetTypeInfo().GetDeclaredMethod("CreateDirectory")!;
                     return (Func<string, object>)mi.CreateDelegate(typeof(Func<string, object>));
-                })!; // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                });
                 createDirectory(path);
-#pragma warning restore CS8634
 
                 return path;
             }
diff --git a/src/System.Private.CoreLib/shared/System/Environment.cs b/src/System.Private.CoreLib/shared/System/Environment.cs
index 319ae9b1c6..d99a5a667a 100644
--- a/src/System.Private.CoreLib/shared/System/Environment.cs
+++ b/src/System.Private.CoreLib/shared/System/Environment.cs
@@ -149,7 +149,7 @@ namespace System
                     versionSpan = versionSpan.Slice(0, separatorIndex);
 
                 // Return zeros rather then failing if the version string fails to parse
-                return Version.TryParse(versionSpan, out Version? version) ? version! : new Version(); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                return Version.TryParse(versionSpan, out Version? version) ? version : new Version();
             }
         }
 
diff --git a/src/System.Private.CoreLib/shared/System/Globalization/CultureData.cs b/src/System.Private.CoreLib/shared/System/Globalization/CultureData.cs
index d29668e173..03875c39c0 100644
--- a/src/System.Private.CoreLib/shared/System/Globalization/CultureData.cs
+++ b/src/System.Private.CoreLib/shared/System/Globalization/CultureData.cs
@@ -359,7 +359,7 @@ namespace System.Globalization
             if (retVal == null || (retVal.IsNeutralCulture == true))
             {
                 // Not a valid mapping, try the hard coded table
-                string name;
+                string? name;
                 if (RegionNames.TryGetValue(cultureName, out name))
                 {
                     // Make sure we can get culture data for it
@@ -590,7 +590,7 @@ namespace System.Globalization
             {
                 // Check the hash table
                 bool ret;
-                CultureData retVal;
+                CultureData? retVal;
                 lock (s_lock)
                 {
                     ret = tempHashTable.TryGetValue(hashName, out retVal);
diff --git a/src/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs b/src/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs
index 2005cf3b73..7b5ae00b69 100644
--- a/src/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs
+++ b/src/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs
@@ -221,8 +221,8 @@ namespace System.Globalization
                     AddIgnorableSymbols(".");
                     return;
                 }
-                string words;
-                if (KnownWords.TryGetValue(str, out words) == false)
+
+                if (KnownWords.TryGetValue(str, out _) == false)
                 {
                     if (m_dateWords == null)
                     {
diff --git a/src/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.Win32.cs b/src/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.Win32.cs
index ffea420e7c..f717adbfe3 100644
--- a/src/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.Win32.cs
+++ b/src/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.Win32.cs
@@ -92,10 +92,10 @@ namespace System.Globalization
             Array.Resize(ref registryEraRanges, iFoundEras);
 
             // Sort them
-            Array.Sort(registryEraRanges!, CompareEraRanges); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            Array.Sort(registryEraRanges, CompareEraRanges);
 
             // Clean up era information
-            for (int i = 0; i < registryEraRanges!.Length; i++) // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            for (int i = 0; i < registryEraRanges.Length; i++)
             {
                 // eras count backwards from length to 1 (and are 1 based indexes into string arrays)
                 registryEraRanges[i].era = registryEraRanges.Length - i;
diff --git a/src/System.Private.CoreLib/shared/System/Globalization/JapaneseLunisolarCalendar.cs b/src/System.Private.CoreLib/shared/System/Globalization/JapaneseLunisolarCalendar.cs
index cdaded6bc3..34631e261e 100644
--- a/src/System.Private.CoreLib/shared/System/Globalization/JapaneseLunisolarCalendar.cs
+++ b/src/System.Private.CoreLib/shared/System/Globalization/JapaneseLunisolarCalendar.cs
@@ -201,7 +201,7 @@ namespace System.Globalization
             // If we didn't copy any then something was wrong, just return base
             if (newIndex == 0) return baseEras;
 
-            Array.Resize(ref newEras!, newIndex); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            Array.Resize(ref newEras!, newIndex);
             return newEras;
         }
 
diff --git a/src/System.Private.CoreLib/shared/System/IO/Stream.cs b/src/System.Private.CoreLib/shared/System/IO/Stream.cs
index 3b63d17a3c..4b3b0d3a06 100644
--- a/src/System.Private.CoreLib/shared/System/IO/Stream.cs
+++ b/src/System.Private.CoreLib/shared/System/IO/Stream.cs
@@ -42,7 +42,7 @@ namespace System.IO
         {
             // Lazily-initialize _asyncActiveSemaphore.  As we're never accessing the SemaphoreSlim's
             // WaitHandle, we don't need to worry about Disposing it.
-            return LazyInitializer.EnsureInitialized<SemaphoreSlim>(ref _asyncActiveSemaphore!, () => new SemaphoreSlim(1, 1)); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            return LazyInitializer.EnsureInitialized(ref _asyncActiveSemaphore, () => new SemaphoreSlim(1, 1));
         }
 
         public abstract bool CanRead
@@ -1061,7 +1061,7 @@ namespace System.IO
             {
                 get
                 {
-                    return LazyInitializer.EnsureInitialized<ManualResetEvent>(ref _waitHandle!, () => new ManualResetEvent(true)); // Remove ! when nullable attributes are respected
+                    return LazyInitializer.EnsureInitialized(ref _waitHandle, () => new ManualResetEvent(true));
                 }
             }
 
diff --git a/src/System.Private.CoreLib/shared/System/Reflection/Assembly.cs b/src/System.Private.CoreLib/shared/System/Reflection/Assembly.cs
index 569c5f5c8c..69820dea99 100644
--- a/src/System.Private.CoreLib/shared/System/Reflection/Assembly.cs
+++ b/src/System.Private.CoreLib/shared/System/Reflection/Assembly.cs
@@ -235,7 +235,7 @@ namespace System.Reflection
 
             string normalizedPath = Path.GetFullPath(path);
 
-            Assembly result;
+            Assembly? result;
             lock (s_loadfile)
             {
                 if (s_loadfile.TryGetValue(normalizedPath, out result))
diff --git a/src/System.Private.CoreLib/shared/System/Resources/ResourceManager.cs b/src/System.Private.CoreLib/shared/System/Resources/ResourceManager.cs
index fbc13b04a3..49e8027ce3 100644
--- a/src/System.Private.CoreLib/shared/System/Resources/ResourceManager.cs
+++ b/src/System.Private.CoreLib/shared/System/Resources/ResourceManager.cs
@@ -400,7 +400,7 @@ namespace System.Resources
                 throw new ArgumentNullException(nameof(culture));
 
             Dictionary<string, ResourceSet>? localResourceSets = _resourceSets;
-            ResourceSet rs;
+            ResourceSet? rs;
             if (localResourceSets != null)
             {
                 lock (localResourceSets)
@@ -509,7 +509,7 @@ namespace System.Resources
             lock (localResourceSets)
             {
                 // If another thread added this culture, return that.
-                ResourceSet lostRace;
+                ResourceSet? lostRace;
                 if (localResourceSets.TryGetValue(cultureName, out lostRace))
                 {
                     if (!object.ReferenceEquals(lostRace, rs))
diff --git a/src/System.Private.CoreLib/shared/System/Resources/ResourceReader.Core.cs b/src/System.Private.CoreLib/shared/System/Resources/ResourceReader.Core.cs
index 36e0f89b21..de6cd86521 100644
--- a/src/System.Private.CoreLib/shared/System/Resources/ResourceReader.Core.cs
+++ b/src/System.Private.CoreLib/shared/System/Resources/ResourceReader.Core.cs
@@ -67,11 +67,11 @@ namespace System.Resources
 
         private void InitializeBinaryFormatter()
         {
-            LazyInitializer.EnsureInitialized<Type>(ref s_binaryFormatterType!, () => // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            LazyInitializer.EnsureInitialized(ref s_binaryFormatterType, () =>
                 Type.GetType("System.Runtime.Serialization.Formatters.Binary.BinaryFormatter, System.Runtime.Serialization.Formatters, Version=0.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a",
                 throwOnError: true)!);
 
-            LazyInitializer.EnsureInitialized<Func<object?,Stream,object>>(ref s_deserializeMethod!, () => // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            LazyInitializer.EnsureInitialized(ref s_deserializeMethod, () =>
             {
                 MethodInfo binaryFormatterDeserialize = s_binaryFormatterType!.GetMethod("Deserialize", new Type[] { typeof(Stream) })!;
 
diff --git a/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/NativeLibrary.cs b/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/NativeLibrary.cs
index 30d50fea7c..2062499057 100644
--- a/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/NativeLibrary.cs
+++ b/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/NativeLibrary.cs
@@ -235,7 +235,7 @@ namespace System.Runtime.InteropServices
                 return IntPtr.Zero;
             }
 
-            if (!s_nativeDllResolveMap.TryGetValue(assembly, out DllImportResolver resolver))
+            if (!s_nativeDllResolveMap.TryGetValue(assembly, out DllImportResolver? resolver))
             {
                 return IntPtr.Zero;
             }
diff --git a/src/System.Private.CoreLib/shared/System/Runtime/Loader/AssemblyLoadContext.cs b/src/System.Private.CoreLib/shared/System/Runtime/Loader/AssemblyLoadContext.cs
index 4bc4ced0b9..230667b3a3 100644
--- a/src/System.Private.CoreLib/shared/System/Runtime/Loader/AssemblyLoadContext.cs
+++ b/src/System.Private.CoreLib/shared/System/Runtime/Loader/AssemblyLoadContext.cs
@@ -248,11 +248,7 @@ namespace System.Runtime.Loader
 
                 foreach (WeakReference<AssemblyLoadContext> weakAlc in alcList)
                 {
-                    AssemblyLoadContext? alc = null;
-
-                    weakAlc.TryGetTarget(out alc);
-
-                    if (alc != null)
+                    if (weakAlc.TryGetTarget(out AssemblyLoadContext? alc))
                     {
                         yield return alc;
                     }
@@ -428,7 +424,7 @@ namespace System.Runtime.Loader
             {
                 foreach (var alcAlive in s_allContexts)
                 {
-                    if (alcAlive.Value.TryGetTarget(out AssemblyLoadContext alc))
+                    if (alcAlive.Value.TryGetTarget(out AssemblyLoadContext? alc))
                     {
                         alc.RaiseUnloadEvent();
                     }
diff --git a/src/System.Private.CoreLib/shared/System/Text/StringBuilder.cs b/src/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
index 165ea4ee2f..81cd160bdc 100644
--- a/src/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
+++ b/src/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
@@ -1987,9 +1987,9 @@ namespace System.Text
                     }
                     else if (replacementsCount >= replacements.Length)
                     {
-                        Array.Resize(ref replacements!, replacements.Length * 3 / 2 + 4); // Grow by ~1.5x, but more in the begining // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                        Array.Resize(ref replacements, replacements.Length * 3 / 2 + 4); // Grow by ~1.5x, but more in the begining
                     }
-                    replacements![replacementsCount++] = indexInChunk; // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                    replacements[replacementsCount++] = indexInChunk;
                     indexInChunk += oldValue.Length;
                     count -= oldValue.Length;
                 }
diff --git a/src/System.Private.CoreLib/shared/System/Threading/ExecutionContext.cs b/src/System.Private.CoreLib/shared/System/Threading/ExecutionContext.cs
index c1cae56594..8345e30d60 100644
--- a/src/System.Private.CoreLib/shared/System/Threading/ExecutionContext.cs
+++ b/src/System.Private.CoreLib/shared/System/Threading/ExecutionContext.cs
@@ -546,7 +546,7 @@ namespace System.Threading
                 {
                     int newNotificationIndex = newChangeNotifications.Length;
                     Array.Resize(ref newChangeNotifications, newNotificationIndex + 1);
-                    newChangeNotifications![newNotificationIndex] = local; // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                    newChangeNotifications[newNotificationIndex] = local;
                 }
             }
 
diff --git a/src/System.Private.CoreLib/shared/System/Threading/LazyInitializer.cs b/src/System.Private.CoreLib/shared/System/Threading/LazyInitializer.cs
index 442e94234d..0ee21a2a70 100644
--- a/src/System.Private.CoreLib/shared/System/Threading/LazyInitializer.cs
+++ b/src/System.Private.CoreLib/shared/System/Threading/LazyInitializer.cs
@@ -48,7 +48,7 @@ namespace System.Threading
         /// if an object was not used and to then dispose of the object appropriately.
         /// </para>
         /// </remarks>
-        public static T EnsureInitialized<T>([AllowNull] ref T target) where T : class =>
+        public static T EnsureInitialized<T>([NotNull] ref T? target) where T : class =>
             Volatile.Read(ref target) ?? EnsureInitializedCore(ref target);
 
         /// <summary>
@@ -57,7 +57,7 @@ namespace System.Threading
         /// <typeparam name="T">The reference type of the reference to be initialized.</typeparam>
         /// <param name="target">The variable that need to be initialized</param>
         /// <returns>The initialized variable</returns>
-        private static T EnsureInitializedCore<T>([AllowNull] ref T target) where T : class
+        private static T EnsureInitializedCore<T>([NotNull] ref T? target) where T : class
         {
             try
             {
@@ -100,7 +100,7 @@ namespace System.Threading
         /// if an object was not used and to then dispose of the object appropriately.
         /// </para>
         /// </remarks>
-        public static T EnsureInitialized<T>([AllowNull] ref T target, Func<T> valueFactory) where T : class =>
+        public static T EnsureInitialized<T>([NotNull] ref T? target, Func<T> valueFactory) where T : class =>
             Volatile.Read(ref target) ?? EnsureInitializedCore(ref target, valueFactory);
 
         /// <summary>
@@ -110,7 +110,7 @@ namespace System.Threading
         /// <param name="target">The variable that need to be initialized</param>
         /// <param name="valueFactory">The delegate that will be executed to initialize the target</param>
         /// <returns>The initialized variable</returns>
-        private static T EnsureInitializedCore<T>([AllowNull] ref T target, Func<T> valueFactory) where T : class
+        private static T EnsureInitializedCore<T>([NotNull] ref T? target, Func<T> valueFactory) where T : class
         {
             T value = valueFactory();
             if (value == null)
@@ -242,7 +242,7 @@ namespace System.Threading
         /// <paramref name="target"/>. If <paramref name="syncLock"/> is null, a new object will be instantiated.</param>
         /// <param name="valueFactory">The <see cref="T:System.Func{T}"/> invoked to initialize the reference.</param>
         /// <returns>The initialized value of type <typeparamref name="T"/>.</returns>
-        public static T EnsureInitialized<T>([AllowNull] ref T target, [NotNull] ref object? syncLock, Func<T> valueFactory) where T : class =>
+        public static T EnsureInitialized<T>([NotNull] ref T? target, [NotNull] ref object? syncLock, Func<T> valueFactory) where T : class =>
             Volatile.Read(ref target) ?? EnsureInitializedCore(ref target, ref syncLock, valueFactory);
 
         /// <summary>
@@ -257,7 +257,7 @@ namespace System.Threading
         /// The <see cref="T:System.Func{T}"/> to invoke in order to produce the lazily-initialized value.
         /// </param>
         /// <returns>The initialized object.</returns>
-        private static T EnsureInitializedCore<T>([AllowNull] ref T target, [NotNull] ref object? syncLock, Func<T> valueFactory) where T : class
+        private static T EnsureInitializedCore<T>([NotNull] ref T? target, [NotNull] ref object? syncLock, Func<T> valueFactory) where T : class
         {
             // Lazily initialize the lock if necessary and then double check if initialization is still required.
             lock (EnsureLockInitialized(ref syncLock))
@@ -272,7 +272,7 @@ namespace System.Threading
                 }
             }
 
-            return target;
+            return target!; // TODO-NULLABLE: Remove ! when nullable attributes are respected
         }
 
         /// <summary>
diff --git a/src/System.Private.CoreLib/shared/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs b/src/System.Private.CoreLib/shared/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
index 7554097b1d..20a375135c 100644
--- a/src/System.Private.CoreLib/shared/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
+++ b/src/System.Private.CoreLib/shared/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
@@ -152,7 +152,7 @@ namespace System.Threading.Tasks
         private CompletionState EnsureCompletionStateInitialized()
         {
             // ValueLock not needed, but it's ok if it's held
-            return LazyInitializer.EnsureInitialized<CompletionState>(ref m_completionState!, () => new CompletionState()); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            return LazyInitializer.EnsureInitialized(ref m_completionState, () => new CompletionState());
         }
 
         /// <summary>Gets whether completion has been requested.</summary>
@@ -382,7 +382,7 @@ namespace System.Threading.Tasks
                 for (int i = 0; i < m_maxItemsPerTask; i++)
                 {
                     // Get the next available exclusive task.  If we can't find one, bail.
-                    Task exclusiveTask;
+                    Task? exclusiveTask;
                     if (!m_exclusiveTaskScheduler.m_tasks.TryDequeue(out exclusiveTask)) break;
 
                     // Execute the task.  If the scheduler was previously faulted,
@@ -430,7 +430,7 @@ namespace System.Threading.Tasks
                 for (int i = 0; i < m_maxItemsPerTask; i++)
                 {
                     // Get the next available concurrent task.  If we can't find one, bail.
-                    Task concurrentTask;
+                    Task? concurrentTask;
                     if (!m_concurrentTaskScheduler.m_tasks.TryDequeue(out concurrentTask)) break;
 
                     // Execute the task.  If the scheduler was previously faulted,
diff --git a/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs b/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs
index 6e8dee7a1b..bf539a52de 100644
--- a/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs
+++ b/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs
@@ -194,7 +194,7 @@ namespace System.Threading.Tasks
         {
             Debug.Assert(task != null, "Null Task objects can't be added to the ActiveTasks collection");
 
-            LazyInitializer.EnsureInitialized<Dictionary<int, Task>>(ref s_currentActiveTasks!, () => new Dictionary<int, Task>()); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            LazyInitializer.EnsureInitialized(ref s_currentActiveTasks, () => new Dictionary<int, Task>());
 
             int taskId = task.Id;
             lock (s_currentActiveTasks)
@@ -1343,7 +1343,7 @@ namespace System.Threading.Tasks
         /// <returns>The initialized contingent properties object.</returns>
         internal ContingentProperties EnsureContingentPropertiesInitialized()
         {
-            return LazyInitializer.EnsureInitialized<ContingentProperties>(ref m_contingentProperties!, () => new ContingentProperties())!; // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            return LazyInitializer.EnsureInitialized(ref m_contingentProperties, () => new ContingentProperties());
         }
 
         /// <summary>
diff --git a/src/System.Private.CoreLib/shared/System/Threading/Thread.cs b/src/System.Private.CoreLib/shared/System/Threading/Thread.cs
index 9707b03499..eeb2f413ce 100644
--- a/src/System.Private.CoreLib/shared/System/Threading/Thread.cs
+++ b/src/System.Private.CoreLib/shared/System/Threading/Thread.cs
@@ -355,7 +355,7 @@ namespace System.Threading
                 Dictionary<string, LocalDataStoreSlot> nameToSlotMap = EnsureNameToSlotMap();
                 lock (nameToSlotMap)
                 {
-                    LocalDataStoreSlot slot;
+                    LocalDataStoreSlot? slot;
                     if (!nameToSlotMap.TryGetValue(name, out slot))
                     {
                         slot = AllocateSlot();
diff --git a/src/System.Private.CoreLib/shared/System/TimeZoneInfo.Unix.cs b/src/System.Private.CoreLib/shared/System/TimeZoneInfo.Unix.cs
index e56144f2f8..88c8893c3f 100644
--- a/src/System.Private.CoreLib/shared/System/TimeZoneInfo.Unix.cs
+++ b/src/System.Private.CoreLib/shared/System/TimeZoneInfo.Unix.cs
@@ -618,7 +618,7 @@ namespace System
             string? id;
             if (TryGetLocalTzFile(out rawData, out id))
             {
-                TimeZoneInfo? result = GetTimeZoneFromTzData(rawData, id!); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                TimeZoneInfo? result = GetTimeZoneFromTzData(rawData, id);
                 if (result != null)
                 {
                     return result;
diff --git a/src/System.Private.CoreLib/shared/System/WeakReference.T.cs b/src/System.Private.CoreLib/shared/System/WeakReference.T.cs
index 6121bdf12c..407c1bd34a 100644
--- a/src/System.Private.CoreLib/shared/System/WeakReference.T.cs
+++ b/src/System.Private.CoreLib/shared/System/WeakReference.T.cs
@@ -52,7 +52,7 @@ namespace System
         //          DoSomething(ref.Target)
         //
         [MethodImplAttribute(MethodImplOptions.AggressiveInlining)]
-        public bool TryGetTarget([MaybeNull, NotNullWhen(true)] out T target)
+        public bool TryGetTarget([MaybeNullWhen(false), NotNullWhen(true)] out T target)
         {
             // Call the worker method that has more performant but less user friendly signature.
             T o = this.Target;
diff --git a/src/System.Private.CoreLib/shared/System/WinRTFolderPaths.cs b/src/System.Private.CoreLib/shared/System/WinRTFolderPaths.cs
index b0986dab09..ae065f0354 100644
--- a/src/System.Private.CoreLib/shared/System/WinRTFolderPaths.cs
+++ b/src/System.Private.CoreLib/shared/System/WinRTFolderPaths.cs
@@ -130,7 +130,7 @@ namespace System
                 case SpecialFolder.System:
                     return SystemDirectory;
                 case SpecialFolder.Windows:
-                    return Path.GetDirectoryName(SystemDirectory)!; // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                    return Path.GetDirectoryName(SystemDirectory)!;
                 default:
                     return string.Empty;
             }
diff --git a/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs b/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs
index 2c4d1a5a27..0a0590b45d 100644
--- a/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs
+++ b/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs
@@ -108,7 +108,7 @@ namespace Internal.Runtime.InteropServices
     {
         // Collection of all ALCs used for COM activation. In the event we want to support
         // unloadable COM server ALCs, this will need to be changed.
-        private static readonly Dictionary<string, AssemblyLoadContext> s_AssemblyLoadContexts = new Dictionary<string, AssemblyLoadContext>(StringComparer.InvariantCultureIgnoreCase);
+        private static readonly Dictionary<string, AssemblyLoadContext> s_assemblyLoadContexts = new Dictionary<string, AssemblyLoadContext>(StringComparer.InvariantCultureIgnoreCase);
 
         /// <summary>
         /// Entry point for unmanaged COM activation API from managed code
@@ -370,14 +370,14 @@ $@"{nameof(UnregisterClassForTypeInternal)} arguments:
 
         private static AssemblyLoadContext GetALC(string assemblyPath)
         {
-            AssemblyLoadContext alc;
+            AssemblyLoadContext? alc;
 
-            lock (s_AssemblyLoadContexts)
+            lock (s_assemblyLoadContexts)
             {
-                if (!s_AssemblyLoadContexts.TryGetValue(assemblyPath, out alc))
+                if (!s_assemblyLoadContexts.TryGetValue(assemblyPath, out alc))
                 {
                     alc = new IsolatedComponentLoadContext(assemblyPath);
-                    s_AssemblyLoadContexts.Add(assemblyPath, alc);
+                    s_assemblyLoadContexts.Add(assemblyPath, alc);
                 }
             }
 
diff --git a/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComponentActivator.cs b/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComponentActivator.cs
index e025413137..42a3838a46 100644
--- a/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComponentActivator.cs
+++ b/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComponentActivator.cs
@@ -15,14 +15,14 @@ namespace Internal.Runtime.InteropServices
 {
     public static class ComponentActivator
     {
-        private static readonly Dictionary<string, IsolatedComponentLoadContext> s_AssemblyLoadContexts;
-        private static readonly Dictionary<IntPtr, Delegate> s_Delegates = new Dictionary<IntPtr, Delegate>();
+        private static readonly Dictionary<string, IsolatedComponentLoadContext> s_assemblyLoadContexts;
+        private static readonly Dictionary<IntPtr, Delegate> s_delegates = new Dictionary<IntPtr, Delegate>();
 
         public delegate int ComponentEntryPoint(IntPtr args, int sizeBytes);
 
         static ComponentActivator()
         {
-            s_AssemblyLoadContexts = new Dictionary<string, IsolatedComponentLoadContext>(StringComparer.InvariantCulture);
+            s_assemblyLoadContexts = new Dictionary<string, IsolatedComponentLoadContext>(StringComparer.InvariantCulture);
         }
 
         private static string MarshalToString(IntPtr arg, string argName)
@@ -91,10 +91,10 @@ namespace Internal.Runtime.InteropServices
 
                 IntPtr functionPtr = Marshal.GetFunctionPointerForDelegate(d);
 
-                lock(s_Delegates)
+                lock(s_delegates)
                 {
                     // Keep a reference to the delegate to prevent it from being garbage collected
-                    s_Delegates[functionPtr] = d;
+                    s_delegates[functionPtr] = d;
                 }
 
                 Marshal.WriteIntPtr(functionHandle, functionPtr);
@@ -126,14 +126,14 @@ namespace Internal.Runtime.InteropServices
 
         private static IsolatedComponentLoadContext GetIsolatedComponentLoadContext(string assemblyPath)
         {
-            IsolatedComponentLoadContext alc;
+            IsolatedComponentLoadContext? alc;
 
-            lock (s_AssemblyLoadContexts)
+            lock (s_assemblyLoadContexts)
             {
-                if (!s_AssemblyLoadContexts.TryGetValue(assemblyPath, out alc))
+                if (!s_assemblyLoadContexts.TryGetValue(assemblyPath, out alc))
                 {
                     alc = new IsolatedComponentLoadContext(assemblyPath);
-                    s_AssemblyLoadContexts.Add(assemblyPath, alc);
+                    s_assemblyLoadContexts.Add(assemblyPath, alc);
                 }
             }
 
diff --git a/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/WindowsRuntime/ActivationFactoryLoader.cs b/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/WindowsRuntime/ActivationFactoryLoader.cs
index 5b691d608d..5c0a9433bb 100644
--- a/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/WindowsRuntime/ActivationFactoryLoader.cs
+++ b/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/WindowsRuntime/ActivationFactoryLoader.cs
@@ -16,18 +16,18 @@ namespace Internal.Runtime.InteropServices.WindowsRuntime
         // Since each of the assemblies that act as the "key" here are WinRT assemblies
         // we don't need to share this dictionary with the COM activation dictionary
         // since there will be no overlap.
-        private static Dictionary<string, AssemblyLoadContext> s_AssemblyLoadContexts = new Dictionary<string, AssemblyLoadContext>(StringComparer.InvariantCultureIgnoreCase);
+        private static readonly Dictionary<string, AssemblyLoadContext> s_assemblyLoadContexts = new Dictionary<string, AssemblyLoadContext>(StringComparer.InvariantCultureIgnoreCase);
         
         private static AssemblyLoadContext GetALC(string assemblyPath)
         {
-            AssemblyLoadContext alc;
+            AssemblyLoadContext? alc;
 
-            lock (s_AssemblyLoadContexts)
+            lock (s_assemblyLoadContexts)
             {
-                if (!s_AssemblyLoadContexts.TryGetValue(assemblyPath, out alc))
+                if (!s_assemblyLoadContexts.TryGetValue(assemblyPath, out alc))
                 {
                     alc = new IsolatedComponentLoadContext(assemblyPath);
-                    s_AssemblyLoadContexts.Add(assemblyPath, alc);
+                    s_assemblyLoadContexts.Add(assemblyPath, alc);
                 }
             }
 
diff --git a/src/System.Private.CoreLib/src/System/Attribute.CoreCLR.cs b/src/System.Private.CoreLib/src/System/Attribute.CoreCLR.cs
index e17f430ebc..96a04fd502 100644
--- a/src/System.Private.CoreLib/src/System/Attribute.CoreCLR.cs
+++ b/src/System.Private.CoreLib/src/System/Attribute.CoreCLR.cs
@@ -390,7 +390,7 @@ namespace System
             for (int i = 0; i < attributes.Length; i++)
             {
                 Type attrType = attributes[i].GetType();
-                AttributeUsageAttribute usage;
+                AttributeUsageAttribute? usage;
                 types.TryGetValue(attrType, out usage);
 
                 if (usage == null)
diff --git a/src/System.Private.CoreLib/src/System/IO/FileLoadException.CoreCLR.cs b/src/System.Private.CoreLib/src/System/IO/FileLoadException.CoreCLR.cs
index 91d933428b..6ec7e893ff 100644
--- a/src/System.Private.CoreLib/src/System/IO/FileLoadException.CoreCLR.cs
+++ b/src/System.Private.CoreLib/src/System/IO/FileLoadException.CoreCLR.cs
@@ -30,7 +30,7 @@ namespace System.IO
             else 
                 GetMessageForHR(hResult, JitHelpers.GetStringHandleOnStack(ref message));
 
-            return string.Format(format!, fileName, message); // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            return string.Format(format, fileName, message);
         }
 
         [DllImport(JitHelpers.QCall, CharSet = CharSet.Unicode)]
diff --git a/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs b/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs
index eae84bf22a..463ea6c865 100644
--- a/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs
+++ b/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs
@@ -80,7 +80,7 @@ namespace System.Reflection
         {
             RuntimeAssembly? retAssembly = null;
             GetExecutingAssemblyNative(JitHelpers.GetStackCrawlMarkHandle(ref stackMark), JitHelpers.GetObjectHandleOnStack(ref retAssembly));
-            return retAssembly!; // TODO-NULLABLE: Remove ! when nullable attributes are respected
+            return retAssembly;
         }
 
         // Get the assembly that the current code is running from.
diff --git a/src/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs b/src/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs
index 042cf510bd..db4fb4a347 100644
--- a/src/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs
+++ b/src/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs
@@ -102,7 +102,7 @@ namespace System.Reflection.Emit
 
         internal void CheckTypeNameConflict(string strTypeName, Type? enclosingType)
         {
-            if (_typeBuilderDict.TryGetValue(strTypeName, out Type foundType) &&
+            if (_typeBuilderDict.TryGetValue(strTypeName, out Type? foundType) &&
                 ReferenceEquals(foundType.DeclaringType, enclosingType))
             {
                 // Cannot have two types with the same name
@@ -224,7 +224,7 @@ namespace System.Reflection.Emit
             }
             else
             {
-                if (_typeBuilderDict.TryGetValue(strTypeName, out Type foundType))
+                if (_typeBuilderDict.TryGetValue(strTypeName, out Type? foundType))
                 {
                     return foundType;
                 }
diff --git a/src/System.Private.CoreLib/src/System/RtType.cs b/src/System.Private.CoreLib/src/System/RtType.cs
index 4d65e3d04d..4277b79b2e 100644
--- a/src/System.Private.CoreLib/src/System/RtType.cs
+++ b/src/System.Private.CoreLib/src/System/RtType.cs
@@ -128,15 +128,14 @@ namespace System
                         _items = new T[_capacity];
                         _items[0] = _item;
                     }
-                    else
-                    if (_capacity == _count)
+                    else if (_capacity == _count)
                     {
                         int newCapacity = 2 * _capacity;
                         Array.Resize(ref _items, newCapacity);
                         _capacity = newCapacity;
                     }
 
-                    _items![_count] = item; // TODO-NULLABLE: Remove ! when nullable attributes are respected
+                    _items![_count] = item;
                 }
                 _count++;
             }
diff --git a/src/System.Private.CoreLib/src/System/Runtime/InteropServices/WindowsRuntime/EventRegistrationTokenTable.cs b/src/System.Private.CoreLib/src/System/Runtime/InteropServices/WindowsRuntime/EventRegistrationTokenTable.cs
index f9eb669b05..b2848c3929 100644
--- a/src/System.Private.CoreLib/src/System/Runtime/InteropServices/WindowsRuntime/EventRegistrationTokenTable.cs
+++ b/src/System.Private.CoreLib/src/System/Runtime/InteropServices/WindowsRuntime/EventRegistrationTokenTable.cs
@@ -152,7 +152,7 @@ namespace System.Runtime.InteropServices.WindowsRuntime
         // Remove the event handler from the table and 
         // Get the delegate associated with an event registration token if it exists
         // If the event registration token is not registered, returns false
-        public bool RemoveEventHandler(EventRegistrationToken token, out T handler)
+        public bool RemoveEventHandler(EventRegistrationToken token, [NotNullWhen(true)] out T? handler)
         {
             lock (m_tokens)
             {
@@ -196,7 +196,7 @@ namespace System.Runtime.InteropServices.WindowsRuntime
                 // value.  Therefore we need to make sure we really have the handler we want before taking the
                 // fast path.
                 EventRegistrationToken preferredToken = GetPreferredToken(handler);
-                T registeredHandler;
+                T? registeredHandler;
                 if (m_tokens.TryGetValue(preferredToken, out registeredHandler))
                 {
                     if (registeredHandler == handler)
@@ -228,7 +228,7 @@ namespace System.Runtime.InteropServices.WindowsRuntime
 
         private void RemoveEventHandlerNoLock(EventRegistrationToken token)
         {
-            T handler;
+            T? handler;
             if (m_tokens.TryGetValue(token, out handler))
             {
                 m_tokens.Remove(token);
diff --git a/src/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyDependencyResolver.cs b/src/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyDependencyResolver.cs
index ad9f585aa5..c2f1bf3ae5 100644
--- a/src/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyDependencyResolver.cs
+++ b/src/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyDependencyResolver.cs
@@ -144,7 +144,7 @@ namespace System.Runtime.Loader
             else if (assemblyName.Name != null)
             {
                 // Load code assembly - simply look it up in the dictionary by its simple name.
-                if (_assemblyPaths.TryGetValue(assemblyName.Name, out string assemblyPath))
+                if (_assemblyPaths.TryGetValue(assemblyName.Name, out string? assemblyPath))
                 {
                     // Only returnd the assembly if it exists on disk - this is to make the behavior of the API
                     // consistent. Resource and native resolutions will only return existing files