code: def validate(self):
          
          if not (isinstance(self.target_class, set) and
                  all(isinstance(x, six.string_types) for x in self.target_class)):
              raise TypeError(u'Expected set of string target_class, got: {} {}'.format(
                  type(self.target_class).__name__, self.target_class))
  
          for cls in self.target_class:
              validate_safe_string(cls)
docs: Ensure that the CoerceType block is valid.