diff --git a/build/psalm-baseline.xml b/build/psalm-baseline.xml
index 114dc479f1a..7de2b7161b8 100644
--- a/build/psalm-baseline.xml
+++ b/build/psalm-baseline.xml
@@ -2980,9 +2980,6 @@
       <code><![CDATA[getAppValue]]></code>
       <code><![CDATA[setAppValue]]></code>
     </DeprecatedMethod>
-    <NullArgument>
-      <code><![CDATA[null]]></code>
-    </NullArgument>
   </file>
   <file src="core/Command/Encryption/MigrateKeyStorage.php">
     <DeprecatedClass>
@@ -4010,9 +4007,6 @@
       <code><![CDATA[false]]></code>
       <code><![CDATA[false]]></code>
     </InvalidArgument>
-    <NullArgument>
-      <code><![CDATA[null]]></code>
-    </NullArgument>
   </file>
   <file src="lib/private/IntegrityCheck/Checker.php">
     <InvalidArrayAccess>
@@ -4389,9 +4383,6 @@
     <InvalidArgument>
       <code><![CDATA[$groupsList]]></code>
     </InvalidArgument>
-    <NullArgument>
-      <code><![CDATA[null]]></code>
-    </NullArgument>
   </file>
   <file src="lib/private/legacy/OC_Helper.php">
     <InvalidArrayOffset>
diff --git a/core/Command/Encryption/Enable.php b/core/Command/Encryption/Enable.php
index 2c476185692..02045fa1a4b 100644
--- a/core/Command/Encryption/Enable.php
+++ b/core/Command/Encryption/Enable.php
@@ -42,8 +42,8 @@ class Enable extends Command {
 			$output->writeln('<error>No encryption module is loaded</error>');
 			return 1;
 		}
-		$defaultModule = $this->config->getAppValue('core', 'default_encryption_module', null);
-		if ($defaultModule === null) {
+		$defaultModule = $this->config->getAppValue('core', 'default_encryption_module');
+		if ($defaultModule === '') {
 			$output->writeln('<error>No default module is set</error>');
 			return 1;
 		}
diff --git a/lib/private/AppConfig.php b/lib/private/AppConfig.php
index a245f3149d2..d023e688c00 100644
--- a/lib/private/AppConfig.php
+++ b/lib/private/AppConfig.php
@@ -1386,15 +1386,15 @@ class AppConfig implements IAppConfig {
 	 *
 	 * @param string $app app
 	 * @param string $key key
-	 * @param string $default = null, default value if the key does not exist
+	 * @param string $default - Default value if the key does not exist
 	 *
-	 * @return ?string the value or $default
+	 * @return string the value or $default
 	 * @deprecated 29.0.0 use getValue*()
 	 *
 	 * This function gets a value from the appconfig table. If the key does
 	 * not exist the default value will be returned
 	 */
-	public function getValue($app, $key, $default = null) {
+	public function getValue($app, $key, $default = '') {
 		$this->loadConfig($app);
 		$this->matchAndApplyLexiconDefinition($app, $key);
 
diff --git a/lib/private/Installer.php b/lib/private/Installer.php
index 91d20a129ae..fd737d286ad 100644
--- a/lib/private/Installer.php
+++ b/lib/private/Installer.php
@@ -546,7 +546,7 @@ class Installer {
 				while (false !== ($filename = readdir($dir))) {
 					if ($filename[0] !== '.' and is_dir($app_dir['path'] . "/$filename")) {
 						if (file_exists($app_dir['path'] . "/$filename/appinfo/info.xml")) {
-							if ($config->getAppValue($filename, 'installed_version', null) === null) {
+							if ($config->getAppValue($filename, 'installed_version') === '') {
 								$enabled = $appManager->isDefaultEnabled($filename);
 								if (($enabled || in_array($filename, $appManager->getAlwaysEnabledApps()))
 									  && $config->getAppValue($filename, 'enabled') !== 'no') {
diff --git a/lib/private/legacy/OC_App.php b/lib/private/legacy/OC_App.php
index 10b78e2a7ef..6dbef42594b 100644
--- a/lib/private/legacy/OC_App.php
+++ b/lib/private/legacy/OC_App.php
@@ -685,7 +685,7 @@ class OC_App {
 		//set remote/public handlers
 		if (array_key_exists('ocsid', $appData)) {
 			\OC::$server->getConfig()->setAppValue($appId, 'ocsid', $appData['ocsid']);
-		} elseif (\OC::$server->getConfig()->getAppValue($appId, 'ocsid', null) !== null) {
+		} elseif (\OC::$server->getConfig()->getAppValue($appId, 'ocsid') !== '') {
 			\OC::$server->getConfig()->deleteAppValue($appId, 'ocsid');
 		}
 		foreach ($appData['remote'] as $name => $path) {
diff --git a/tests/Core/Command/Encryption/EnableTest.php b/tests/Core/Command/Encryption/EnableTest.php
index 32d1a7576f5..0e9655c29c7 100644
--- a/tests/Core/Command/Encryption/EnableTest.php
+++ b/tests/Core/Command/Encryption/EnableTest.php
@@ -48,9 +48,9 @@ class EnableTest extends TestCase {
 
 	public static function dataEnable(): array {
 		return [
-			['no', null, [], true, 'Encryption enabled', 'No encryption module is loaded'],
-			['yes', null, [], false, 'Encryption is already enabled', 'No encryption module is loaded'],
-			['no', null, ['OC_TEST_MODULE' => []], true, 'Encryption enabled', 'No default module is set'],
+			['no', '', [], true, 'Encryption enabled', 'No encryption module is loaded'],
+			['yes', '', [], false, 'Encryption is already enabled', 'No encryption module is loaded'],
+			['no', '', ['OC_TEST_MODULE' => []], true, 'Encryption enabled', 'No default module is set'],
 			['no', 'OC_NO_MODULE', ['OC_TEST_MODULE' => []], true, 'Encryption enabled', 'The current default module does not exist: OC_NO_MODULE'],
 			['no', 'OC_TEST_MODULE', ['OC_TEST_MODULE' => []], true, 'Encryption enabled', 'Default module: OC_TEST_MODULE'],
 		];
@@ -79,7 +79,7 @@ class EnableTest extends TestCase {
 				->method('getAppValue')
 				->willReturnMap([
 					['core', 'encryption_enabled', 'no', $oldStatus],
-					['core', 'default_encryption_module', null, $defaultModule],
+					['core', 'default_encryption_module', '', $defaultModule],
 				]);
 		}