@classmethod
def simple_user_exists(cls, *args, **kwargs):
    """
        Return True/False if a User instance exists with the given arguments.
        Arguments are directly passed to filter() manager method.
        TODO: consider how to ensure case-insensitive email matching
        """
    kwargs = cls.username_field(kwargs)
    return cls.user_model().objects.filter(*args, **kwargs).exists()
