Code assumes that details.get(USERNAME) will return a string. That's not the case...

Code assumes that details.get(USERNAME) will return a string. That's not the case with the dropbox backend (which returns an int) and possibly others. Without casting to a string we'll get an error on line 45. The other alternative is to call username_fixer prior to the short_username change, which could do the cast for backends that require it.