Validate a :class:`dict` of values. If `self.schema` is falsy this
        is a noop.

def validate(self, values):
        """Validate a :class:`dict` of values. If `self.schema` is falsy this
        is a noop.
        """
        if not self.schema or (values is None and not self.schema.get('required', False)):
            return
        self.validator.validate(values)