Error on only random questions

When assigning only random questions from a choosen term and zero static questions, I get the following error:

warning: Invalid argument supplied for foreach() in /var/www/html/public/_testomgeving/quiz/sites/all/modules/quiz/quiz.admin.inc on line 367.

The variable $form_state['values']['weights'] in line 367 is NULL.

I don't get this error if I have at least one static question (with the same random settings). So I assume it's because there are no static questions (which could have weight) but only random questions (which can't have weight). But since I am not a programmer, I could be wrong here.

MySQL 5.0.45 | PHP 5.2.4