You're using an outdated version of LimeSurvey. Please update to the latest version and check if the bug can still be reproduced. Thank you.

I now tested it on version 4.4.11+210301 and the bug is still there. I also tested the described solution and it also worked in this version.

Can you enable debug = 2 in application/config/config.php and try again, please? Paste the complete error message here.

As you told me, I enabled the debug mode, then I specified a 'error_log' destination and there are no errors showing. I even put a test 'error_log()' in the functions that are related to the problem and they are shown as expected.

Thanks! We will look closer.

Wait, how does your suggested fix interact with default values?

Maybe it's better to check for === null?

Okay I checkt your suggestion and It solves the problem and is slimmer. So you can just do it like this:

protected function setDefaultIfEmpty($value, $default)
{
if(is_null($value)) {
return $default;
}
return trim($value) == '' ? $default : $value;
}

Thanks for the help!

Fix committed to master branch: http://bugs.limesurvey.org/plugin.php?page=Source/view&id=31494