feat(expect): added null as positive value for toBeOptionalOf

[npwork]

Description (What)

It would be nice to have null as a positive value(as well as undefined) for toBeOptionalOf

Justification (Why)

There are cases when object received from server (dto) has null as a value. In this case toBeOptionalOf fails which not correct. It should treat null the same way as undefined

How Can This Be Tested?

[JamieMason]

Thanks a lot, on my mobile just now but what I would want to do is instead put this behaviour in a new matcher called toBeNilOf, and maybe also add a toBeNullable of. This is just so it doesn't surprise anyone - although null means "nothing" it is still the presence of a value (even if that value describes nothing) - whereas undefined is the absence of a value.

Really hope that makes sense 😬