code: private function getFieldArgTypeNode($type, $fieldName, $argName)
      {
          $fieldArgNode = $this->getFieldArgNode($type, $fieldName, $argName);
  
          return $fieldArgNode ? $fieldArgNode->type : null;
      }
docs: @param ObjectType|InterfaceType $type
  @param string                   $fieldName
  @param string                   $argName
  
  @return TypeNode|null