diff --git a/src/WebDAV/ByteMarkWebDAVServerTest.php b/src/WebDAV/ByteMarkWebDAVServerTest.php
index 2014084c7..3940ac88f 100644
--- a/src/WebDAV/ByteMarkWebDAVServerTest.php
+++ b/src/WebDAV/ByteMarkWebDAVServerTest.php
@@ -10,7 +10,7 @@ class ByteMarkWebDAVServerTest extends WebDAVAdapterTestCase
 {
     protected static function createFilesystemAdapter(): FilesystemAdapter
     {
-        if ($_ENV['TEST_WEBDAV'] !== 'YES') {
+        if (($_ENV['TEST_WEBDAV'] ?? '') !== 'YES') {
             self::markTestSkipped('Library regression');
         }
         $client = new UrlPrefixingClientStub(['baseUri' => 'http://localhost:4080/', 'userName' => 'alice', 'password' => 'secret1234']);