code: def _get_queue_name(cls, queue_name=None):
          
          if queue_name is None and cls.queue_name is None:
              raise LimpydJobsException("Queue's name not defined")
          if queue_name is None:
              return cls.queue_name
          return queue_name
docs: Return the given queue_name if defined, else the class's one.
          If both are None, raise an Exception