System.Collections.* missed Equals nullable annotations

src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs

@@ -143,7 +143,7 @@ public void CopyTo(int sourceIndex, T[] destination, int destinationIndex, int l
         public void CopyTo(T[] destination) { }
         public void CopyTo(T[] destination, int destinationIndex) { }
         public bool Equals(System.Collections.Immutable.ImmutableArray<T> other) { throw null; }
-        public override bool Equals(object? obj) { throw null; }
+        public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] object? obj) { throw null; }
         public System.Collections.Immutable.ImmutableArray<T>.Enumerator GetEnumerator() { throw null; }
         public override int GetHashCode() { throw null; }
         public int IndexOf(T item) { throw null; }

src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Minimal.cs

@@ -306,7 +306,7 @@ public override int GetHashCode()
         /// <returns>
         ///   <c>true</c> if the specified <see cref="object"/> is equal to this instance; otherwise, <c>false</c>.
         /// </returns>
-        public override bool Equals(object? obj)
+        public override bool Equals([NotNullWhen(true)] object? obj)
         {
             return obj is IImmutableArray other && this.array == other.Array;
         }

src/libraries/System.Collections.Specialized/ref/System.Collections.Specialized.cs

@@ -18,7 +18,7 @@ public partial struct BitVector32
         public static int CreateMask(int previous) { throw null; }
         public static System.Collections.Specialized.BitVector32.Section CreateSection(short maxValue) { throw null; }
         public static System.Collections.Specialized.BitVector32.Section CreateSection(short maxValue, System.Collections.Specialized.BitVector32.Section previous) { throw null; }
-        public override bool Equals(object? o) { throw null; }
+        public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] object? o) { throw null; }
         public override int GetHashCode() { throw null; }
         public override string ToString() { throw null; }
         public static string ToString(System.Collections.Specialized.BitVector32 value) { throw null; }
@@ -28,7 +28,7 @@ public readonly partial struct Section
             public short Mask { get { throw null; } }
             public short Offset { get { throw null; } }
             public bool Equals(System.Collections.Specialized.BitVector32.Section obj) { throw null; }
-            public override bool Equals(object? o) { throw null; }
+            public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] object? o) { throw null; }
             public override int GetHashCode() { throw null; }
             public static bool operator ==(System.Collections.Specialized.BitVector32.Section a, System.Collections.Specialized.BitVector32.Section b) { throw null; }
             public static bool operator !=(System.Collections.Specialized.BitVector32.Section a, System.Collections.Specialized.BitVector32.Section b) { throw null; }

src/libraries/System.Collections.Specialized/src/System/Collections/Specialized/BitVector32.cs

@@ -3,6 +3,7 @@
 
 using System.Diagnostics;
 using System.Text;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Collections.Specialized
 {
@@ -184,7 +185,7 @@ private static Section CreateSectionHelper(short maxValue, short priorMask, shor
             return new Section(CreateMaskFromHighValue(maxValue), offset);
         }
 
-        public override bool Equals(object? o)
+        public override bool Equals([NotNullWhen(true)] object? o)
         {
             if (!(o is BitVector32))
             {
@@ -253,7 +254,7 @@ public short Offset
                 }
             }
 
-            public override bool Equals(object? o)
+            public override bool Equals([NotNullWhen(true)] object? o)
             {
                 if (o is Section)
                     return Equals((Section)o);

src/libraries/System.Collections/src/System/Collections/Generic/SortedSetEqualityComparer.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace System.Collections.Generic
 {
     /// <summary>
@@ -47,7 +49,7 @@ public int GetHashCode(SortedSet<T> obj)
         }
 
         // Equals method for the comparer itself.
-        public override bool Equals(object? obj)
+        public override bool Equals([NotNullWhen(true)] object? obj)
         {
             SortedSetEqualityComparer<T>? comparer = obj as SortedSetEqualityComparer<T>;
             return comparer != null && _comparer == comparer._comparer;