MDL-30742 restoring 1.9 backups with missing question data should be robust

question/type/multichoice/backup/moodle1/lib.php

@@ -50,6 +50,21 @@ class moodle1_qtype_multichoice_handler extends moodle1_qtype_handler {
         }
 
         // convert and write the multichoice
+        if (!isset($data['multichoice'])) {
+            // This should never happen, but it can do if the 1.9 site contained
+            // corrupt data/
+            $data['multichoice'] = array(array(
+                'single'                         => 1,
+                'shuffleanswers'                 => 1,
+                'correctfeedback'                => '',
+                'correctfeedbackformat'          => FORMAT_HTML,
+                'partiallycorrectfeedback'       => '',
+                'partiallycorrectfeedbackformat' => FORMAT_HTML,
+                'incorrectfeedback'              => '',
+                'incorrectfeedbackformat'        => FORMAT_HTML,
+                'answernumbering'                => 'abc',
+            ));
+        }
         $this->write_multichoice($data['multichoice'], $data['oldquestiontextformat']);
     }
 

question/type/multichoice/backup/moodle2/restore_qtype_multichoice_plugin.class.php

@@ -73,7 +73,11 @@ class restore_qtype_multichoice_plugin extends restore_qtype_plugin {
             // Adjust some columns
             $data->question = $newquestionid;
             // Map sequence of question_answer ids
-            $answersarr = explode(',', $data->answers);
+            if ($data->answers) {
+                $answersarr = explode(',', $data->answers);
+            } else {
+                $answersarr = array();
+            }
             foreach ($answersarr as $key => $answer) {
                 $answersarr[$key] = $this->get_mappingid('question_answer', $answer);
             }