Cannot read property 'root' of null 解决方法

运行一个ReactNative程序，结果出现这种情况..

看终端的输出信息是：

 ┌────────────────────────────────────────────────────────────────────────────┐ 

 │  Running packager on port 8081.                                            │ 

 │                                                                            │ 

 │  Keep this packager running while developing on any JS projects. Feel      │ 

 │  free to close this tab and run your own packager instance if you          │ 

 │  prefer.                                                                   │ 

 │                                                                            │ 

 │  https://github.com/facebook/react-native                                  │ 

 │                                                                            │ 

 └────────────────────────────────────────────────────────────────────────────┘ 

Looking for JS files in

   /Users/mac/codebox/AwesomeProject1231 

React packager ready.

[11:25:37] fs crawl

TypeError: Cannot read property 'root' of null

    at /Users/mac/codebox/AwesomeProject1231/node_modules/react-native/packager/react-packager/src/DependencyResolver/crawlers/index.js:16:84

    at tryCallOne (/Users/mac/codebox/AwesomeProject1231/node_modules/react-native/node_modules/promise/lib/core.js:37:12)

    at /Users/mac/codebox/AwesomeProject1231/node_modules/react-native/node_modules/promise/lib/core.js:103:15

    at flush (/Users/mac/codebox/AwesomeProject1231/node_modules/react-native/node_modules/promise/node_modules/asap/raw.js:50:29)

    at doNTCallback0 (node.js:408:9)

    at process._tickCallback (node.js:337:13)

[11:26:10] request:/index.ios.bundle

[11:26:10] find dependencies

解决方法：

打开终端，输入 

brew update

成功后再输入

brew upgrade watchman

关掉Xcode重新运行即可

如果你这么就解决问题了就好了.. 我自己brew update的时候遇到这样的问题

No such file or directory - /usr/local/Library/Formula/.brew.67541.1327099610

解决方法：

依次输入

sudo chown -R $USER:admin /usr/local

cd /usr/local

git reset --hard origin/master

brew update

再brew upgrade watchman

最后：