From 5fbbb51882e3a5ee4fe2cd454efd61dbd76711b0 Mon Sep 17 00:00:00 2001
From: Andrew Nicols <andrew@nicols.co.uk>
Date: Fri, 6 Jan 2023 21:10:51 +0800
Subject: [PATCH] MDL-76362 core: Use empty default string when getting prefs

The json_decode function does not accept a null, which is the
traditional default for get_user_preferences. By passing a default of
am empty string we avoid issues in PHP 8.1.
---
 course/format/classes/base.php | 2 +-
 lib/tablelib.php               | 5 ++---
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/course/format/classes/base.php b/course/format/classes/base.php
index bc8a6d69ef7..26000882a46 100644
--- a/course/format/classes/base.php
+++ b/course/format/classes/base.php
@@ -608,7 +608,7 @@ abstract class base {
         $course = $this->get_course();
         try {
             $sectionpreferences = (array) json_decode(
-                get_user_preferences('coursesectionspreferences_' . $course->id, null, $USER->id) ?? ''
+                get_user_preferences("coursesectionspreferences_{$course->id}", '', $USER->id)
             );
             if (empty($sectionpreferences)) {
                 $sectionpreferences = [];
diff --git a/lib/tablelib.php b/lib/tablelib.php
index bf099cd9066..b9b593a7ffa 100644
--- a/lib/tablelib.php
+++ b/lib/tablelib.php
@@ -573,7 +573,7 @@ class flexible_table {
         global $SESSION;
         if (isset($SESSION->flextable[$uniqueid])) {
             $prefs = $SESSION->flextable[$uniqueid];
-        } else if (!$prefs = json_decode(get_user_preferences('flextable_' . $uniqueid), true)) {
+        } else if (!$prefs = json_decode(get_user_preferences("flextable_{$uniqueid}", ''), true)) {
             return '';
         }
 
@@ -1463,7 +1463,7 @@ class flexible_table {
 
         // Load any existing user preferences.
         if ($this->persistent) {
-            $this->prefs = json_decode(get_user_preferences('flextable_' . $this->uniqueid) ?? '', true);
+            $this->prefs = json_decode(get_user_preferences("flextable_{$this->uniqueid}", ''), true);
             $oldprefs = $this->prefs;
         } else if (isset($SESSION->flextable[$this->uniqueid])) {
             $this->prefs = $SESSION->flextable[$this->uniqueid];
@@ -2346,4 +2346,3 @@ class table_dataformat_export_format extends table_default_export_format_parent
         exit();
     }
 }
-