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]
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]
[11:26:10]
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：
