code: final public function clear($fieldName)
      {
          $this->guardFrozenMessage();
          $field = static::schema()->getField($fieldName);
          unset($this->data[$fieldName]);
          $this->clearedFields[$fieldName] = true;
          $this->populateDefault($field);
          return $this;
      }
docs: {@inheritdoc}
  @return static