Feedback warnings and errors on response page OU 975809

[emanoylov]

When a Questionnaire uses Feedback Sections without questions, the View your response(s) page displays these warnings/errors after a student completes the questionnaire.

Warning: Undefined variable $sectionlabel in /var/www/html/moodle/mod/questionnaire/questionnaire.class.php on line 4402

Warning: Undefined variable $output in /var/www/html/moodle/mod/questionnaire/drawchart.php on line 294

Exception - implode(): If argument #1 ($separator) is of type string, argument #2 ($array) must be of type array, null given

Steps to reproduce:

• As an admin, create a new Questionnaire
• Add a question that supports feedback e.g. Yes/No question
• Click Feedback
• In Feedback option, select Feedback sections
• Choose a Chart type e.g. Horizontal bars
• Click Save settings and edit Feedback Sections
• Add a new label but do not add any questions in the “Add question to section” field
• Save changes
• As a student, answer the questionnaire
• Click Continue to view the responses

Additionally the provider class has a small change which was forced by the code checker to order the class implements alphabetically.