New return nil cop

[Ana06]

return and return nil are the same thing, so return nil should be avoided. A new cop to check this would be great! 😉

[rrosenblum]

This cop should be configurable to support the implicit nil (return) and the explicit nil (return nil).

[danielkman]

Hey, I'd like to try and submit a PR for it

[pocke]

#4638
@danielkman Thanks, but a pull-request for this issue is already opened.

[bbatsov]

return and return nil are the same thing, so return nil should be avoided. A new cop to check this would be great!

I can see why some people would want to make this uniform, but I for instance always use return when I just want to get out from some place in a method (meaning the return is in void context and no one cares about it) and return nil if I actually want to explicitly return nil.