From eb12428324d6b2b6af00ae4c9d4dbf7e5c12ec52 Mon Sep 17 00:00:00 2001
From: Paul Holden <paulh@moodle.com>
Date: Wed, 29 Mar 2023 17:59:32 +0100
Subject: [PATCH] MDL-77770 gradereport_user: fix errors when no users to
 navigate.

---
 grade/report/user/renderer.php | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/grade/report/user/renderer.php b/grade/report/user/renderer.php
index 07f7dc8332a..1191026a5b6 100644
--- a/grade/report/user/renderer.php
+++ b/grade/report/user/renderer.php
@@ -142,6 +142,7 @@ class gradereport_user_renderer extends plugin_renderer_base {
 
         $navigationdata = [];
 
+        $users = [];
         while ($userdata = $gui->next_user()) {
             $users[$userdata->user->id] = $userdata->user;
         }
@@ -150,6 +151,11 @@ class gradereport_user_renderer extends plugin_renderer_base {
         $arraykeys = array_keys($users);
         $keynumber = array_search($userid, $arraykeys);
 
+        // Without a valid user or users list, there's nothing to render.
+        if ($keynumber === false) {
+            return '';
+        }
+
         // Determine directionality so that icons can be modified to suit language.
         $previousarrow = right_to_left() ? 'right' : 'left';
         $nextarrow = right_to_left() ? 'left' : 'right';