[FIX] Fixed bug that caused error if an object was undefined

Author: emschwartz

lib/suites/draft-04/keywords/required.js

@@ -10,6 +10,11 @@ module.exports = function(config) {
   var missing = [];
   for (var i = 0, len = config.schema.required.length; i !== len; ++i) {
     var prop = config.schema.required[i];
+    
+    if (!config.inst) {
+      config.inst = {};
+    }
+
     if (!Object.prototype.hasOwnProperty.call(config.inst, prop)) {
       missing.push(prop);
     }