def METHOD_NAME(
    user_id: str
) -> List[learner_group_domain.LearnerGroup]:
    """Returns a list of learner groups of the given facilitator.
    Args:
        user_id: str. The id of the facilitator.
    Returns:
        list(LearnerGroup). A list of learner groups of the given facilitator.
    """
    learner_grp_models = (
        learner_group_models.LearnerGroupModel.get_by_facilitator_id(user_id))
    if not learner_grp_models:
        return []
    return [
        learner_group_services.get_learner_group_from_model(model)
        for model in learner_grp_models
    ]