def next_trials(self):
        """Provides a batch of Trial objects to be queued into the TrialRunner.

        A batch ends when self._trial_generator returns None.

        Returns:
            trials (list): Returns a list of trials.
        """
        trials = []

        for trial in self._trial_generator:
            if trial is None:
                return trials
            trials += [trial]

        self._finished = True
        return trials