After installing new Extjs 4.2, I found that the "save" method of a model stops to work.

I found a minor difference between "buildUrl" in this version:

4.1:
if (me.appendId && id)

4.2:
if (me.appendId && (id != null))

This is in the "Ext.data.proxy.Rest"  definition object.
The bug results in a malformed url like: /posts/.json instead of /posts.json