code: def Validate(self, value):
      
      # Allow None as a default.
      if value is None:
        return
  
      if not isinstance(value, self.rdfclass):
        # Try to coerce the type to the correct rdf_class.
        try:
          return self.rdfclass(value)
        except rdfvalue.InitializeError:
          raise TypeValueError("Value for arg %s should be an %s" %
                               (self.name, self.rdfclass.__name__))
  
      return value
docs: Validate an RDFValue instance.
  
      Args:
        value: An RDFValue instance or something which may be used to instantiate
          the correct instance.
  
      Raises:
        TypeValueError: If the value is not a valid RDFValue instance or the
          required type.
  
      Returns:
        A Valid RDFValue instance.