code: def _cast_message(self, message=None):
          '''Convert message data to :class:`Message` if needed, and
          merge with the default message.
  
          :param message: Message to merge with the default message.
          :rtype: :class:`Message`
          '''
          if message is None:
              message = {}
          if isinstance(message, Mapping):
              message = Message.load_message(message)
          return message.load_from(self.message, verify=Truef _cast_message(self, message=None):
          '''Convert message data to :class:`Message` if needed, and
          merge with the default message.
  
          :param message: Message to merge with the default message.
          :rtype: :class:`Message`
          '''
          if message is None:
              message = {}
          if isinstance(message, Mapping):
              message = Message.load_message(message)
          return message.load_from(self.message, verify=True)
docs: Convert message data to :class:`Message` if needed, and
          merge with the default message.
  
          :param message: Message to merge with the default message.
          :rtype: :class:`Message`