All types for that nil is a valid value can be annotated to exclude nil as a valid value with the not nil annotation
Either I confuse things very much or the sentence should sound: All types for that nil is not a valid value
Aaah, a valid value for the kind of type but not valid value for the context.
Thanks, I got it now.
I think it was at least partially my fault not to have understood the sentence initially.
Nevertheless, it might be a good idea to improve the wording of this sentence. However, this should be done by a native speaker.