message_body is required to send messages with loc_key, loc_args

[allanlei]

To send a message using body_loc_key, body_loc_args, title_loc_key or title_loc_args, the message_body kwargs must be set to non-empty.

According to FCM docs, body(message_body) is optional. It was my understanding that body and body_loc_key+body_loc_args are independent.

The condition check in question:
https://github.com/olucurious/PyFCM/blob/master/pyfcm/baseapi.py#L133

My current workaround to use body_loc_key and body_loc_args is

notify_multiple_devices(
        registration_ids=[],
        message_body=' ',    // single space string
        body_loc_key='mykey',
        body_loc_args=['a', 'b', 'c'],
    )