Mojo JS Bindings: fix the demos

mojo/public/js/codec.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 define("mojo/public/js/codec", [
   "mojo/public/js/unicode",
   "mojo/public/js/buffer",
 ], function(unicode, buffer) {
 
   var kErrorUnsigned = "Passing negative value to unsigned";
@@ skipping 107 matching lines @@
     if (!offset)
       return 0;
     return offsetPointer + offset;
   };
 
   Decoder.prototype.decodeAndCreateDecoder = function(pointer) {
     return new Decoder(this.buffer, this.handles, pointer);
   };
 
   Decoder.prototype.decodeHandle = function() {
-    return this.handles[this.readUint32()];
+    return this.handles[this.readUint32()] || null;
   };
 
   Decoder.prototype.decodeString = function() {
     var numberOfBytes = this.readUint32();
     var numberOfElements = this.readUint32();
     var base = this.next;
     this.next += numberOfElements;
     return unicode.decodeUtf8String(
         new Uint8Array(this.buffer.arrayBuffer, base, numberOfElements));
   };
@@ skipping 681 matching lines @@
   exports.NullablePointerTo = NullablePointerTo;
   exports.ArrayOf = ArrayOf;
   exports.NullableArrayOf = NullableArrayOf;
   exports.PackedBool = PackedBool;
   exports.Handle = Handle;
   exports.NullableHandle = NullableHandle;
   exports.MapOf = MapOf;
   exports.NullableMapOf = NullableMapOf;
   return exports;
 });