From 6ecfb590775ec01c5a72f42e117bfcacb4cabb5e Mon Sep 17 00:00:00 2001
From: Ilya Tregubov <ilya@moodle.com>
Date: Wed, 9 Jun 2021 06:06:10 +0200
Subject: [PATCH] MDL-70750 mod_survey: Fix warning for undefined offset.

---
 lib/graphlib.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/graphlib.php b/lib/graphlib.php
index 64db34af792..11aad5f2070 100644
--- a/lib/graphlib.php
+++ b/lib/graphlib.php
@@ -307,7 +307,7 @@ class graph {
         //print "$thisX, $thisY <br />";
 
         if (($bar!='none') && (string)$thisY != 'none') {
-            if ($relatedset = $this->offset_relation[$set]) {                               // Moodle
+            if (isset($this->offset_relation[$set]) && $relatedset = $this->offset_relation[$set]) {
                 $yoffset = $this->calculated['y_plot'][$relatedset][$index];                // Moodle
             } else {                                                                        // Moodle
                 $yoffset = 0;                                                               // Moodle