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.

def get_messages(self, file_name=None):
        """
        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.
        """
        if file_name is None:
            return self.messages

        elif file_name in self.messages:
            return self.messages[file_name]

        else:
            return []