docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'value') and self.value is not None:
              _dict['value'] = self.value
          if hasattr(self, 'metadata') and self.metadata is not None:
              _dict['metadata'] = self.metadata
          if hasattr(self, 'value_type') and self.value_type is not None:
              _dict['type'] = self.value_type
          if hasattr(self, 'synonyms') and self.synonyms is not None:
              _dict['synonyms'] = self.synonyms
          if hasattr(self, 'patterns') and self.patterns is not None:
              _dict['patterns'] = self.patterns
          if hasattr(self, 'created') and self.created is not None:
              _dict['created'] = datetime_to_string(self.created)
          if hasattr(self, 'updated') and self.updated is not None:
              _dict['updated'] = datetime_to_string(self.updated)
          return _dict