Validate value.
        Args:
          value:
        Returns:
          A validated value.
        Raises:
          UnitError

def validate(self, value):
        """ Validate value.
        Args:
          value:
        Returns:
          A validated value.
        Raises:
          UnitError
        """
        for validate in self.validates:
            value = validate(value)
        return value