diff --git a/lib/private/Files/Storage/DAV.php b/lib/private/Files/Storage/DAV.php
index 0c9c41a3d9..cf715ed174 100644
--- a/lib/private/Files/Storage/DAV.php
+++ b/lib/private/Files/Storage/DAV.php
@@ -143,7 +143,7 @@ class DAV extends Common {
 			'userName' => $this->user,
 			'password' => $this->password,
 		];
-		if (isset($this->authType)) {
+		if ($this->authType !== null) {
 			$settings['authType'] = $this->authType;
 		}
 
diff --git a/lib/private/Route/Router.php b/lib/private/Route/Router.php
index 71bc4a6c4f..3c897c5ce4 100644
--- a/lib/private/Route/Router.php
+++ b/lib/private/Route/Router.php
@@ -95,7 +95,7 @@ class Router implements IRouter {
 	 * @return string[]
 	 */
 	public function getRoutingFiles() {
-		if (!isset($this->routingFiles)) {
+		if ($this->routingFiles === null) {
 			$this->routingFiles = [];
 			foreach (\OC_APP::getEnabledApps() as $app) {
 				$appPath = \OC_App::getAppPath($app);
diff --git a/lib/private/User/User.php b/lib/private/User/User.php
index 24082926b0..c16af5c590 100644
--- a/lib/private/User/User.php
+++ b/lib/private/User/User.php
@@ -128,7 +128,7 @@ class User implements IUser {
 	 * @return string
 	 */
 	public function getDisplayName() {
-		if (!isset($this->displayName)) {
+		if ($this->displayName === null) {
 			$displayName = '';
 			if ($this->backend && $this->backend->implementsActions(Backend::GET_DISPLAYNAME)) {
 				// get display name and strip whitespace from the beginning and end of it