Resolve PR comments

src/ImageSharp/Memory/Allocators/Internals/Gen2GcCallback.cs

@@ -42,7 +42,7 @@ internal sealed class Gen2GcCallback : CriticalFinalizerObject
             // Execute the callback method.
             try
             {
-                if (this.callback1 is not null && !this.callback1(targetObj))
+                if (!this.callback1!(targetObj))
                 {
                     // If the callback returns false, this callback object is no longer needed.
                     this.weakTargetObj.Free();
@@ -63,7 +63,7 @@ internal sealed class Gen2GcCallback : CriticalFinalizerObject
             // Execute the callback method.
             try
             {
-                if (this.callback0 is not null && !this.callback0())
+                if (!this.callback0!())
                 {
                     // If the callback returns false, this callback object is no longer needed.
                     return;

src/ImageSharp/Memory/Allocators/Internals/ManagedBufferBase.cs

@@ -43,5 +43,5 @@ internal abstract class ManagedBufferBase<T> : MemoryManager<T>
     /// Gets the object that should be pinned.
     /// </summary>
     /// <returns>The pinnable <see cref="object"/>.</returns>
-    protected abstract object? GetPinnableObject();
+    protected abstract object GetPinnableObject();
 }

src/ImageSharp/Memory/Allocators/Internals/SharedArrayPoolBuffer{T}.cs

@@ -40,7 +40,11 @@ internal class SharedArrayPoolBuffer<T> : ManagedBufferBase<T>, IRefCounted
         return MemoryMarshal.Cast<byte, T>(this.Array.AsSpan(0, this.lengthInBytes));
     }
 
-    protected override object? GetPinnableObject() => this.Array;
+    protected override object GetPinnableObject()
+    {
+        Guard.NotNull(this.Array);
+        return this.Array;
+    }
 
     public void AddRef()
     {

src/ImageSharp/Memory/Buffer2D{T}.cs

@@ -43,7 +43,7 @@ public sealed class Buffer2D<T> : IDisposable
     /// Gets the backing <see cref="IMemoryGroup{T}"/>.
     /// </summary>
     /// <returns>The MemoryGroup.</returns>
-    public IMemoryGroup<T>? MemoryGroup => this.FastMemoryGroup.View;
+    public IMemoryGroup<T> MemoryGroup => this.FastMemoryGroup.View;
 
     /// <summary>
     /// Gets the backing <see cref="MemoryGroup{T}"/> without the view abstraction.

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.cs

@@ -41,7 +41,7 @@ internal abstract partial class MemoryGroup<T> : IMemoryGroup<T>, IDisposable
     /// <inheritdoc />
     public bool IsValid { get; private set; } = true;
 
-    public MemoryGroupView<T>? View { get; private set; }
+    public MemoryGroupView<T> View { get; private set; } = null!;
 
     /// <inheritdoc />
     public abstract Memory<T> this[int index] { get; }