diff --git a/src/NullCarbon.php b/src/NullCarbon.php
index 3730050..0e611ac 100755
--- a/src/NullCarbon.php
+++ b/src/NullCarbon.php
@@ -41,7 +41,7 @@ public function __construct($time = null, $tz = null)
      */
     public function format($format)
     {
-        return null;
+        return '';
     }
 
     /**