'Return a message header fragment dict.
Args:
request_id (str or None) : message ID of the message this message replies to
Returns:
dict : a message header'

@classmethod
def create_header(cls, request_id=None):

    header = {'msgid': bkserial.make_id(), 'msgtype': cls.msgtype}
    if (request_id is not None):
        header['reqid'] = request_id
    return header
