Converting null literal or possible null value to non-nullable type.

Converting null literal or possible null value to non-nullable type.

Possible null reference argument for parameter 'item' in 'void Stack<IBrush>.Push(IBrush item)'.

Argument of type 'Stack<IBrush>' cannot be used for parameter 'stack' of type 'Stack<IBrush?>' in 'IBrush? StackExtensions.PopOrDefault<IBrush?>(Stack<IBrush?> stack, IBrush? defaultValue)' due to differences in the nullability of reference types.

Converting null literal or possible null value to non-nullable type.

Cannot convert null literal to non-nullable reference type.

Converting null literal or possible null value to non-nullable type.

Converting null literal or possible null value to non-nullable type.

Possible null reference argument for parameter 'item' in 'void Stack<IBrush>.Push(IBrush item)'.