Which PHP version do you use?

@dregad your changes in 0029846 broke PHP 5.5 compatibility. Scalar type hints are supported starting from PHP 7.0

I am using PHP Version 5.6.25

@pbeaumadier as a quick workaround, changing line 678 in file core/summary_api.php
from

 function summary_print_by_project( array $p_projects = array(), int $p_level = 0, array $p_cache = null, array $p_filter = null ) {

to

 function summary_print_by_project( array $p_projects = array(), $p_level = 0, array $p_cache = null, array $p_filter = null ) {

should fix the issue. (didn't try)

Thanks, I will try it right now and let you know

So I can confirm it fixes this issue.
No more error 500, no more error in the logs, the application works fine now.

Thanks a lot.

@dregad your changes in 0029846 broke PHP 5.5 compatibility. Scalar type hints are supported starting from PHP 7.0

Sorry about that, will fix.

Hello,
I am upgrading my Mantis from 1.2.19 to 2.25.4 and I had another problem due to the same reason.
My PHP version is 5.6.25.
My Mantis seems to work even if my upgrade is not still finished (some of my plugins have to be upgraded), so the tests are in progress.
The problem occurs when I wanted to load the summary page and I got a blank page, without error.
In /XXX/log/php-error.log, I found "PHP Fatal error: Default value for parameters with a class type hint can only be NULL in /XXX/core/summary_api.php on line 678.
Applying the modification fixed the problem.
Thank you.