When creating a quizz, only use cloze sub-question with 0 as a grade.
In /question/type/multianswer/question.php, you get a division by zero in get_max_fraction().
Then when starting the quizz, you get a database error :
Default exception handler: Error writing to database Debug: Unknown column 'NAN' in 'field list'\nINSERT INTO mdl_question_attempts[...]
It only happens with PHP 7.