From d311cab0c0e8e7abb042bdc22766699362764269 Mon Sep 17 00:00:00 2001
From: Marina Glancy <marina@moodle.com>
Date: Sat, 26 Nov 2022 14:02:32 +0100
Subject: [PATCH] MDL-76493 core: make sure format_string(null) works on PHP
 8.1

---
 lib/tests/weblib_test.php | 4 ++++
 lib/weblib.php            | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/lib/tests/weblib_test.php b/lib/tests/weblib_test.php
index a6c6aa9b3c3..0663cc84e67 100644
--- a/lib/tests/weblib_test.php
+++ b/lib/tests/weblib_test.php
@@ -48,6 +48,10 @@ class weblib_test extends advanced_testcase {
         // Unicode entities.
         $this->assertSame("&#4475;", format_string("&#4475;"));
 
+        // Nulls.
+        $this->assertSame('', format_string(null));
+        $this->assertSame('', format_string(null, true, ['escape' => false]));
+
         // < and > signs.
         $originalformatstringstriptags = $CFG->formatstringstriptags;
 
diff --git a/lib/weblib.php b/lib/weblib.php
index c3354e559af..374b162e161 100644
--- a/lib/weblib.php
+++ b/lib/weblib.php
@@ -1430,6 +1430,11 @@ function reset_text_filters_cache($phpunitreset = false) {
 function format_string($string, $striplinks = true, $options = null) {
     global $CFG, $PAGE;
 
+    if ($string === '' || is_null($string)) {
+        // No need to do any filters and cleaning.
+        return '';
+    }
+
     // We'll use a in-memory cache here to speed up repeated strings.
     static $strcache = false;