This error happened when a student tried to resume a questionnaire. 

Moodle version: 3.11.12
PHP 8.0

What I think happens is $a is initialized to an empty string ''. Then later it tries to assign $a->number and $a->precision to $a which is not an object but a (empty) string. I guess $a = '' should be replaced by $a = new \stdClass();

Stack Trace:

• line 106 of /mod/questionnaire/classes/question/numerical.php: Error thrown
• line 862 of /mod/questionnaire/classes/question/question.php: call to mod_questionnaire\question\numerical->question_survey_display()
• line 228 of /mod/questionnaire/classes/output/renderer.php: call to mod_questionnaire\question\question->question_output()
• line 1337 of /mod/questionnaire/questionnaire.class.php: call to mod_questionnaire\output\renderer->question_output()
• line 1249 of /mod/questionnaire/questionnaire.class.php: call to questionnaire->survey_render()
• line 281 of /mod/questionnaire/questionnaire.class.php: call to questionnaire->print_survey()
• line 82 of /mod/questionnaire/complete.php: call to questionnaire->view()