[Devpack Compiler] Nullable

[Jim8y]

This pr completes the nullable. This pr fixed and tested some of the nullable methods, but more work need to be done. So this pr can be considered to be part of the job.

However, i am not able to complete it in one pr, its too complex and need to carefully check the compiler, will take a while. Thus, i will consider this pr as has completed its target.

[shargon]

Blocked by?

[Jim8y]

@shargon good to go

[shargon]

@Jim8y ut fault