@staticmethod
def p_if_data_frame_parameter_optional_list(p):
    """if_data_frame_optional_list : if_data_frame_optional
                                       | if_data_frame_optional if_data_frame_optional_list"""
    try:
        p[0] = [p[1]] + p[2]
    except IndexError:
        p[0] = [p[1]]
