JsonPretty seems to break with documents containing null

[pcarrier]

As soon as I try to open a document containing null from the Browser tab, the JavaScript console logs Uncaught JsonPretty error: Cannot read property 'constructor' of null.

It's pretty easy to reproduce with:

curl -XPOST localhost:9200/test/head/a -d '{"foo":null}'
curl -XPOST localhost:9200/test/head/b -d '{"foo":0}'

a fails, b opens just fine.

Reproduced with:

• the current HEAD of master (5b1d5cced6d7f01bd7f1f5e75991a65031ff3056)
• elasticsearch 0.20.4 from homebrew
• Google Chrome 26.0.1410.12 dev.