@staticmethod
def _create_emulator(mode):
    """Create emulator for specified mode.

        If no emulator is specified, we will use the Rasa NLU format."""
    if mode is None:
        from chatbot_nlu.emulators import NoEmulator
        return NoEmulator()
    elif mode.lower() == 'wit':
        from chatbot_nlu.emulators.wit import WitEmulator
        return WitEmulator()
    elif mode.lower() == 'luis':
        from chatbot_nlu.emulators.luis import LUISEmulator
        return LUISEmulator()
    elif mode.lower() == 'dialogflow':
        from chatbot_nlu.emulators.dialogflow import DialogflowEmulator
        return DialogflowEmulator()
    else:
        raise ValueError('unknown mode : {0}'.format(mode))
