private function getDirectiveArgTypeNode(Directive $directive, $argName)
    {
        $argNode = $this->getAllDirectiveArgNodes($directive, $argName)[0];

        return $argNode ? $argNode->type : null;
    }
private function getDirectiveArgTypeNode(Directive $directive, $argName)
    {
        $argNode = $this->getAllDirectiveArgNodes($directive, $argName)[0];

        return $argNode ? $argNode->type : null;
    }
@param string $argName

@return TypeNode|null