def do_execute(self):
        """
        The actual execution of the actor.

        :return: None if successful, otherwise error message
        :rtype: str
        """
        generator = datagen.DataGenerator.make_copy(self.resolve_option("setup"))
        generator.dataset_format = generator.define_data_format()
        if bool(self.resolve_option("incremental")) and generator.single_mode_flag:
            for i in range(generator.num_examples_act):
                self._output.append(Token(generator.generate_example()))
        else:
            data = generator.generate_examples()
            self._output.append(Token(data))
        return None
The actual execution of the actor.

        :return: None if successful, otherwise error message
        :rtype: str