diff --git a/lib/private/Files/Filesystem.php b/lib/private/Files/Filesystem.php
index b85554ae333..3ad518b3950 100644
--- a/lib/private/Files/Filesystem.php
+++ b/lib/private/Files/Filesystem.php
@@ -813,7 +813,7 @@ class Filesystem {
 
 		$cacheKey = json_encode([$path, $stripTrailingSlash, $isAbsolutePath, $keepUnicode]);
 
-		if (isset(self::$normalizedPathCache[$cacheKey])) {
+		if ($cacheKey && isset(self::$normalizedPathCache[$cacheKey])) {
 			return self::$normalizedPathCache[$cacheKey];
 		}