Properly handle the case when a non-string is being validated.
Properly handle the case when a non-string is being validated.

Previously this would trigger 500 error when the parent request structure was
correct, but one of the leafs was a dict instead of a str.

vodkina/GlobaLeaks,vodkina/GlobaLeaks,vodkina/GlobaLeaks,vodkina/GlobaLeaks