MDL-56912 feedback: empty multichoice questions do not submit

mod/feedback/item/feedback_item_class.php

@@ -181,6 +181,7 @@ abstract class feedback_item_base {
      * If it is important which mode the form is in, use $form->get_mode()
      *
      * Each item type must add a single form element with the name $item->typ.'_'.$item->id
+     * This element must always be present in form data even if nothing is selected (i.e. use advcheckbox and not checkbox).
      * To add an element use either:
      * $form->add_form_element() - adds a single element to the form
      * $form->add_form_group_element() - adds a group element to the form

mod/feedback/item/multichoice/lib.php

@@ -349,11 +349,16 @@ class feedback_item_multichoice extends feedback_item_base {
                 }
             } else {
                 // Radio.
+                if (!array_key_exists(0, $options)) {
+                    // Always add '0' as hidden element, otherwise form submit data may not have this element.
+                    $objs[] = ['hidden', $inputname.'[0]'];
+                }
                 foreach ($options as $idx => $label) {
                     $objs[] = ['radio', $inputname.'[0]', '', $label, $idx];
                 }
                 $element = $form->add_form_group_element($item, 'group_'.$inputname, $name, $objs, $separator, $class);
                 $form->set_element_default($inputname.'[0]', $tmpvalue);
+                $form->set_element_type($inputname.'[0]', PARAM_INT);
             }
         }
 

mod/feedback/item/multichoicerated/lib.php

@@ -302,12 +302,17 @@ class feedback_item_multichoicerated extends feedback_item_base {
                     ['select', $inputname, $name, array('' => '') + $options, array('class' => $class)]);
         } else {
             $objs = array();
+            if (!array_key_exists(0, $options)) {
+                // Always add '0' as hidden element, otherwise form submit data may not have this element.
+                $objs[] = ['hidden', $inputname];
+            }
             foreach ($options as $idx => $label) {
                 $objs[] = ['radio', $inputname, '', $label, $idx];
             }
             $separator = $info->horizontal ? ' ' : '<br>';
             $class .= ' multichoicerated-' . ($info->horizontal ? 'horizontal' : 'vertical');
             $el = $form->add_form_group_element($item, 'group_'.$inputname, $name, $objs, $separator, $class);
+            $form->set_element_type($inputname, PARAM_INT);
 
             // Set previously input values.
             $form->set_element_default($inputname, $form->get_item_value($item));