docs: def get_message(zelf):
          """
          get one message if available else return None
          if message is available returns the result of handler(message)
          does not block!
  
          if you would like to call your handler manually, this is the way to
          go. don't pass in a handler to Listener() and the default handler will
          log and return the message for your own manual processing
          """
          try:
              message = zelf.r.master.rpoplpush(zelf.lijst, zelf._processing)
              if message:
                  # NOTE(tr3buchet): got a message, process it
                  LOG.debug('received: |%s|' % message)
                  return zelf._call_handler(message)
          except zelf.r.generic_error:
              LOG.exception('')