code: private function invalidReturnTypeError(
          ObjectType $returnType,
          $result,
          $fieldNodes
      ) {
          return new Error(
              'Expected value of type "' . $returnType->name . '" but got: ' . Utils::printSafe($result) . '.',
              $fieldNodes
          );
      }
docs: @param mixed[]     $result
  @param FieldNode[] $fieldNodes
  
  @return Error