Fixed unused_display_options

behaviourtype.php

@@ -47,4 +47,12 @@ class qbehaviour_certaintywithstudentfeedback_type extends qbehaviour_certaintyw
     public function can_questions_finish_during_the_attempt() {
         return true;
     }
+
+    /**
+     * {@inheritDoc}
+     * @see question_behaviour_type::get_unused_display_options()
+     */
+    public function get_unused_display_options() {
+        return array();
+    }
 }
\ No newline at end of file