diff --git a/Model/Theme.php b/Model/Theme.php
index 2a23d540..8110d150 100644
--- a/Model/Theme.php
+++ b/Model/Theme.php
@@ -70,7 +70,7 @@ public function __construct(string $name, string $path)
      */
     public function __toString(): string
     {
-        return $this->title ?: $this->name;
+        return (string) ($this->title ?: $this->name);
     }
 
     /**