Argument of type 'Func<T, Rope<char>>' cannot be used for parameter 'itemToString' of type 'Func<T?, Rope<char>>' in 'Rope<char> CompatibilityExtensions.DiffEncode<T>(Rope<T> items, Func<T?, Rope<char>> itemToString, char separator = '~')' due to differences in the nullability of reference types.

Argument of type 'Func<T, Rope<char>>' cannot be used for parameter 'itemToString' of type 'Func<T?, Rope<char>>' in 'Rope<char> CompatibilityExtensions.DiffEncode<T>(Rope<T> items, Func<T?, Rope<char>> itemToString, char separator = '~')' due to differences in the nullability of reference types.

Dereference of a possibly null reference.

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

Argument of type 'Func<T, Rope<char>>' cannot be used for parameter 'itemToString' of type 'Func<T?, Rope<char>>' in 'Rope<char> CompatibilityExtensions.DiffEncode<T>(Rope<T> items, Func<T?, Rope<char>> itemToString, char separator = '~')' due to differences in the nullability of reference types.

Dereference of a possibly null reference.