diff --git a/lib/models/utils/unfix-type.js b/lib/models/utils/unfix-type.js
index cd9b602..ac8ac27 100644
--- a/lib/models/utils/unfix-type.js
+++ b/lib/models/utils/unfix-type.js
@@ -1,4 +1,4 @@
-module.exports = function unfixType(t) {
+module.exports = function unfixType(t = '') {
   return t.replace(/^(String|Boolean|Number|Any|Void|Null|Undefined|Object)$/g, function(match) {
     return match.toLowerCase();
   });