After an Ubuntu release upgrade from 18.04.1 LTS to 20.04.1 LTS, my SQL server was upgraded from 5.7.32 to 8.0.22 version.
The PHP was also upgraded from 7.3 to 7.4 version.
My existing mantis website (2.22.1 - DB 209) works fine with the new environment
but if i try to upgrade Mantis to a more recent version, I get an INTERNAL APPLICATION ERROR during the mantis DB upgrade 
:Call to a member function BindTimeStamp() on null\n/var/www/mantis-bc/admin/schema.php: 69:
- - - - installer_db_now()\n/var/www/mantis-bc/config/config_inc.php: 2:
- - - - include( <string>'/var/www/mantis-bc/admin/schema.php' )\n/var/www/mantis-bc/core.php: 105:
- - - - require_once( <string>'/var/www/mantis-bc/config/config_inc.php' )\n/var/www/mantis-bc/admin/install.php: 34:
- - - - require_once( <string>'/var/www/mantis-bc/core.php' )\n, referer: http://<myserver>/mantis-bc/login_page.php
Any clue about this BindTimeStamp function called by installer_db_now() ? Any suggestion is welcome...
Thanks in advance.