Check missing to check in haystack

I'm not sure but I think this check if the $needle is inside the $haystack is missing to the work.

Adding @davert in cc because I discovered this issue while trying to use his: https://github.com/Codeception/Codeception/blob/2.0/src/Codeception/Module/REST.php#L447-L455

that is mentioned in this documentation: http://codeception.com/docs/10-WebServices