Access denied for user 'www-data'@'localhost' (using password: NO)

Access denied for user 'www-data'@'localhost' (using password: NO) 
When I am installing, this happen when I click continues

URL: https://my_ip/TravianT4/install/process.php  (it is HTTPS) 

`    Access denied for user 'www-data'@'localhost' (using password: NO)`
