Fixed 'None' and 'NoReturn' bug in inferring router.

[synchronizing]

Fixes #172.

Note that the comparison must be done using type since None is a special typehint case. Python documentation states:

Note that None as a type hint is a special case and is replaced by type(None)."

Referenced here.

[synchronizing]

@dmontagu Any chance you could take a look at this?

[yuval9313]

I have slayed this bug in this PR

[dmontagu]

Closing this now that this return type annotation is used in newer versions of FastAPI.

Please let me know if this addresses other issues not handled by FastAPI and I should re-add support.