/**
* @param string $type
* @param string|null $fileName
*
* @return string
*/
public function render($type, $fileName = null)
{
$generator = new StringGenerator();
if ($fileName === null) {
$fileName = sys_get_temp_dir() . '/' . $generator->generateRandomString();
}
$this->graph->export($type, $fileName);
return file_get_contents($fileName);
}