After upgrading to v12.1.6, sudo openproject configure failed.

$ sudo openproject configure
Launching installer for openproject...
Selected addons: legacy-installer openproject-edition postgres apache2 repositories smtp memcached openproject
[legacy-installer] ./bin/configure
[openproject-edition] ./bin/configure
DONE
[postgres] ./bin/configure
Trying to connect through password-based authentication...
psql command not present. Skipping check.
Postgres connection OK
DONE
[apache2] ./bin/configure
DONE
[repositories] ./bin/configure
DONE
[smtp] ./bin/configure
DONE
[memcached] ./bin/configure
DONE
[openproject] ./bin/configure
DONE
[legacy-installer] ./bin/preinstall
[openproject-edition] ./bin/preinstall
[postgres] ./bin/preinstall
INFO: autoinstall=reuse. Skipping to next step.
[apache2] ./bin/preinstall
[repositories] ./bin/preinstall
Module perl already enabled
Module dav already enabled
Considering dependency dav for dav_svn:
Module dav already enabled
Module dav_svn already enabled
Your MPM seems to be threaded. Selecting cgid instead of cgi.
Module cgid already enabled
[smtp] ./bin/preinstall
[memcached] ./bin/preinstall
[openproject] ./bin/preinstall
[legacy-installer] ./bin/postinstall
[openproject-edition] ./bin/postinstall
[postgres] ./bin/postinstall
[apache2] ./bin/postinstall
Last prefix was /
Module rewrite already enabled
Considering dependency setenvif for ssl:
Module setenvif already enabled
Considering dependency mime for ssl:
Module mime already enabled
Considering dependency socache_shmcb for ssl:
Module socache_shmcb already enabled
Module ssl already enabled
Module proxy already enabled
Considering dependency proxy for proxy_http:
Module proxy already enabled
Module proxy_http already enabled
Module headers already enabled
Module expires already enabled
Considering dependency filter for deflate:
Module filter already enabled
Module deflate already enabled
Module filter already enabled
Site openproject already enabled
AH00526: Syntax error on line 1 of /etc/openproject/addons/apache2/includes/vhost/ssl_ca.conf:
SSLCACertificateFile: file '/etc/ssl/certs' does not exist or is empty
Action 'configtest' failed.
The Apache error log may have more information.
ERROR: apache config check failed. See above.

Indeed ssl_ca.conf file has an error:

SSLCACertificateFile /etc/ssl/certs