MDL-50218 lti: Return empty grade when none exists

mod/lti/servicelib.php

@@ -217,14 +217,11 @@ function lti_read_grade($ltiinstance, $userid) {
     if (!empty($ltigrade) && isset($grades) && isset($grades->items[0]) && is_array($grades->items[0]->grades)) {
         foreach ($grades->items[0]->grades as $agrade) {
             $grade = $agrade->grade;
-            $grade = $grade / $ltigrade;
-            break;
+            if (isset($grade)) {
+                return $grade / $ltigrade;
+            }
         }
     }
-
-    if (isset($grade)) {
-        return $grade;
-    }
 }
 
 function lti_delete_grade($ltiinstance, $userid) {

mod/lti/upgrade.txt

@@ -1,5 +1,10 @@
 This files describes API changes in the lti code.
 
+=== 3.1 ===
+
+* When requesting a grade from the outcome service, and empty grade will now be returned as
+  an empty grade in accordance with the spec. Previously a grade of 0 would be returned.
+
 === 3.0 ===
 
 * Function lti_view (locallib.php) was renamed to lti_launch_tool.