I have upgrade my site form 1.9.3 to 1.9.4 and update php version from 5.6 to 7.2. In php version 5.6 both admin and front working fine but on php 7.2 front working fine, but when i login into admin it shows me blank screen. There is no any error,warning or notice and not any log created. please see the screenshot.
Enable developers mode in file index.php and try to login again. It is likely that after turning on developer mode, you will see an error