diff --git a/CHANGELOG.md b/CHANGELOG.md
index c59c71670..f421172cb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 
+## [Unreleased]
+
+### Fixed
+
+- [645](https://github.com/owncloud/richdocuments/pull/645) - Give the remaining app config settings an empty-string default, so opening a document no longer logs a PHP deprecation on every open
+
 ## [4.3.1] - 2026-09-22
 
 ### Security
@@ -209,7 +215,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 ## [2.4.0] - 2020-07-30
 
 
-[Unreleased]: https://github.com/owncloud/richdocuments/compare/v4.2.0...master
+[Unreleased]: https://github.com/owncloud/richdocuments/compare/v4.3.1...master
 [4.2.0]: https://github.com/owncloud/richdocuments/compare/v4.1.0...v4.2.0
 [4.1.0]: https://github.com/owncloud/richdocuments/compare/v4.0.0...v4.1.0
 [4.0.0]: https://github.com/owncloud/richdocuments/compare/v3.0.1...v4.0.0
diff --git a/lib/AppConfig.php b/lib/AppConfig.php
index 068ff2f8a..6e03a26f1 100644
--- a/lib/AppConfig.php
+++ b/lib/AppConfig.php
@@ -29,6 +29,11 @@ class AppConfig {
 		'zotero' => 'false',
 		'watermark_text' => '',
 		'test_server_groups' => '',
+		'edit_groups' => '',
+		'wopi_url' => '',
+		'test_wopi_url' => '',
+		'doc_format' => '',
+		'menu_option' => '',
 		'canonical_webroot' => '',
 	];
 
diff --git a/tests/unit/AppConfigTest.php b/tests/unit/AppConfigTest.php
index 81002841c..32e4d4a61 100644
--- a/tests/unit/AppConfigTest.php
+++ b/tests/unit/AppConfigTest.php
@@ -50,6 +50,32 @@ public function testOpenInNewtabDefault() {
 		$this->assertEquals(true, $enterpriseEdition);
 	}
 
+	public function stringSettingProvider() {
+		return [
+			['edit_groups'],
+			['wopi_url'],
+			['test_wopi_url'],
+			['doc_format'],
+			['menu_option'],
+		];
+	}
+
+	/**
+	 * Settings holding a string must default to an empty string, never to null,
+	 * so that consumers passing them to string functions do not run into the
+	 * PHP 8.1 deprecation of null arguments.
+	 *
+	 * @dataProvider stringSettingProvider
+	 */
+	public function testStringSettingDefaultsToEmptyString($key) {
+		$this->config->expects($this->once())
+			->method('getAppValue')
+			->with('richdocuments', $key, $this->identicalTo(''))
+			->willReturn('');
+
+		$this->assertSame('', $this->appConfig->getAppValue($key));
+	}
+
 	public function enterpriseFeaturesEnabledProvider() {
 		return [
 			[true, 'false', true],