Validate ``value`` and then use the document's class to unwrap the
            value

def unwrap(self, value, fields=None, session=None):
        ''' Validate ``value`` and then use the document's class to unwrap the
            value'''
        self.validate_unwrap(value, fields=fields, session=session)
        return self.type.unwrap(value, fields=fields, session=session)