Don't break if no attribute value

Fixes the transformation of things like `<button disabled>`.

npm-jsx_whitespace_transformer/package.json

@@ -1,7 +1,7 @@
 {
   "name": "jsx_whitespace_transformer",
   "description": "A utility to update your JSX to behave identically in React 0.8 and React 0.9.",
-  "version": "1.0.0",
+  "version": "1.0.1",
   "main": "run.js",
   "dependencies": {
     "esprima-fb": "~2001.1001.0-dev-harmony-fb",

npm-jsx_whitespace_transformer/transforms/react.js

@@ -20,7 +20,9 @@ var utils = require('jstransform/src/utils');
 
 function visitReactTag(traverse, object, path, state) {
   object.attributes.forEach(function(attr, index) {
-    traverse(attr.value, path, state);
+    if (attr.value) {
+      traverse(attr.value, path, state);
+    }
   });
 
   object.children.forEach(function(child, index) {