Expected type '{__iter__}', got 'None' instead (?!)

Hello!

I'm having a pretty hard time eliminating these warnings from my code, but the latest puts the cherry. I have the following:

(path, contents) = ('bin', os.listdir('bin')) if os.path.exists('bin') else (None, None)

if path is not None:
    validate_path(path, contents) 

In validate path, I get this warning stating that path is none. How on earth could it be None if there's an explicit check that it's NOT none. What could I do to eliminate this warning? I got no response elsewhere... Oh btw the code works correctly so I guess this 

Thank you!