diff --git a/src/Saver/FileSaver.php b/src/Saver/FileSaver.php
index 5aae88c..264ab81 100644
--- a/src/Saver/FileSaver.php
+++ b/src/Saver/FileSaver.php
@@ -14,7 +14,7 @@ public function __construct($file)
 
     public function isSupported()
     {
-        return is_writable(dirname($this->file));
+        return $this->file && is_writable(dirname($this->file));
     }
 
     public function save(array $data)