diff --git a/src/Model/User.php b/src/Model/User.php
index cb769ce3fc..ed63d67650 100644
--- a/src/Model/User.php
+++ b/src/Model/User.php
@@ -675,6 +675,10 @@ class User
 	 */
 	public static function updateLastActivity(int $uid)
 	{
+		if (!$uid) {
+			return;
+		}
+
 		$user = User::getById($uid, ['last-activity']);
 		if (empty($user)) {
 			return;
@@ -1640,7 +1644,7 @@ class User
 	 */
 	public static function identities(int $uid): array
 	{
-		if (empty($uid)) {
+		if (!$uid) {
 			return [];
 		}
 
@@ -1651,7 +1655,7 @@ class User
 			return $identities;
 		}
 
-		if ($user['parent-uid'] == 0) {
+		if (!$user['parent-uid']) {
 			// First add our own entry
 			$identities = [[
 				'uid' => $user['uid'],
@@ -1712,7 +1716,7 @@ class User
 	 */
 	public static function hasIdentities(int $uid): bool
 	{
-		if (empty($uid)) {
+		if (!$uid) {
 			return false;
 		}
 
@@ -1721,7 +1725,7 @@ class User
 			return false;
 		}
 
-		if ($user['parent-uid'] != 0) {
+		if ($user['parent-uid']) {
 			return true;
 		}
 
@@ -1848,8 +1852,8 @@ class User
 	{
 		$condition = [
 			'email'           => self::getAdminEmailList(),
-			'parent-uid'      => 0,
-			'blocked'         => 0,
+			'parent-uid'      => null,
+			'blocked'         => false,
 			'verified'        => true,
 			'account_removed' => false,
 			'account_expired' => false,
diff --git a/src/Module/Delegation.php b/src/Module/Delegation.php
index 3595ff7f30..8a2b313000 100644
--- a/src/Module/Delegation.php
+++ b/src/Module/Delegation.php
@@ -53,7 +53,7 @@ class Delegation extends BaseModule
 			}
 		}
 
-		$identity = intval($_POST['identity'] ?? 0);
+		$identity = intval($request['identity'] ?? 0);
 		if (!$identity) {
 			return;
 		}
@@ -76,16 +76,16 @@ class Delegation extends BaseModule
 			$user = DBA::selectFirst('user', [], ['uid' => $identity, 'parent-uid' => $orig_record['uid']]);
 
 			// Check if the target user is one of our siblings
-			if (!DBA::isResult($user) && ($orig_record['parent-uid'] != 0)) {
+			if (!DBA::isResult($user) && $orig_record['parent-uid']) {
 				$user = DBA::selectFirst('user', [], ['uid' => $identity, 'parent-uid' => $orig_record['parent-uid']]);
 			}
 
 			// Check if it's our parent or our own user
 			if (!DBA::isResult($user)
 				&& (
-					$orig_record['parent-uid'] != 0 && $orig_record['parent-uid'] == $identity
+					$orig_record['parent-uid'] && $orig_record['parent-uid'] === $identity
 					||
-					$orig_record['uid'] != 0 && $orig_record['uid'] == $identity
+					$orig_record['uid'] && $orig_record['uid'] === $identity
 				)
 			) {
 				$user = User::getById($identity);
diff --git a/src/Module/Settings/Delegation.php b/src/Module/Settings/Delegation.php
index 134b002c1b..3fd5fef49f 100644
--- a/src/Module/Settings/Delegation.php
+++ b/src/Module/Settings/Delegation.php
@@ -43,11 +43,13 @@ class Delegation extends BaseSettings
 
 		BaseModule::checkFormSecurityTokenRedirectOnError('settings/delegation', 'delegate');
 
-		$parent_uid = (int)$_POST['parent_user'] ?? 0;
-		$parent_password = $_POST['parent_password'] ?? '';
+		$parent_uid = $request['parent_user'] ?? null;
+		$parent_password = $request['parent_password'] ?? '';
 
-		if ($parent_uid != 0) {
+		if ($parent_uid) {
 			try {
+				// An integer value will trigger the direct user query on uid in User::getAuthenticationInfo
+				$parent_uid = (int)$parent_uid;
 				User::getIdFromPasswordAuthentication($parent_uid, $parent_password);
 				DI::sysmsg()->addInfo(DI::l10n()->t('Delegation successfully granted.'));
 			} catch (\Exception $ex) {
@@ -142,7 +144,7 @@ class Delegation extends BaseSettings
 			$parents = [0 => DI::l10n()->t('No parent user')];
 
 			$fields = ['uid', 'username', 'nickname'];
-			$condition = ['email' => $user['email'], 'verified' => true, 'blocked' => false, 'parent-uid' => 0];
+			$condition = ['email' => $user['email'], 'verified' => true, 'blocked' => false, 'parent-uid' => null];
 			$parent_users = DBA::selectToArray('user', $fields, $condition);
 			foreach($parent_users as $parent) {
 				if ($parent['uid'] != DI::userSession()->getLocalUserId()) {
diff --git a/tests/src/Model/UserTest.php b/tests/src/Model/UserTest.php
index eb0cb9f32f..939d282455 100644
--- a/tests/src/Model/UserTest.php
+++ b/tests/src/Model/UserTest.php
@@ -82,7 +82,7 @@ class UserTest extends MockedTest
 	public function testIdentitiesAsParent()
 	{
 		$parentSelect               = $this->parent;
-		$parentSelect['parent-uid'] = 0;
+		$parentSelect['parent-uid'] = null;
 
 		// Select the user itself (=parent)
 		$this->dbMock->shouldReceive('selectFirst')->with('user',