def __init__(self, identifier, datatype, default=None, optional=True, mutable=False):
        if _debug:
            OptionalProperty._debug("__init__ %s %s default=%r optional=%r mutable=%r",
                identifier, datatype, default, optional, mutable
                )

        # continue with the initialization
        StandardProperty.__init__(self, identifier, datatype, default, optional, mutable)