diff --git a/lib/request.js b/lib/request.js
index b99c373..141c1ca 100644
--- a/lib/request.js
+++ b/lib/request.js
@@ -513,7 +513,7 @@ module.exports = {
 
   is: function(types){
     // no request body
-    if (!(this.length || 'transfer-encoding' in this.header)) return null;
+    if (!(this.length || 'transfer-encoding' in this.header)) return;
 
     var ct = this.type;
     // no content-type