Address inconsistent-return-statements
    
    Pylint warns about inconsistent return statements when some paths of a
    function return None implicitly. Make all implicit returns either
    explicit or raise a proper exception.
    
    See: https://pagure.io/freeipa/issue/7758
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>