code: public function isTypeOf($value, $context, ResolveInfo $info)
      {
          return isset($this->config['isTypeOf']) ? call_user_func(
              $this->config['isTypeOf'],
              $value,
              $context,
              $info
          ) : null;
      }
docs: @param mixed[]      $value
  @param mixed[]|null $context
  
  @return bool|null