@classmethod
def unwrap(cls, value, default=None):
    if (value is None):
        return default
    elif isinstance(value, cls):
        return None
    else:
        return value
@classmethod
def unwrap(cls, value, default=None):
    if (value is None):
        return default
    elif isinstance(value, cls):
        return None
    else:
        return value