code: def is_first(self, value):
          
          if value == self._defaults['ai.session.isFirst'] and 'ai.session.isFirst' in self._values:
              del self._values['ai.session.isFirst']
          else:
              self._values['ai.session.isFirst'] = value
docs: The is_first property.
          
          Args:
              value (string). the property value.