code: def get_messages(self, file_name=None):
          
          if file_name is None:
              return self.messages
  
          elif file_name in self.messages:
              return self.messages[file_name]
  
          else:
              return []
docs: Return messages for a file (if file_name provided).
          If file_name is none, returns all messages as a dict.
          :param file_name:
          :return: array if file_name is provided, dict otherwise.