ractivejs/ractive — pull request #1567 by Rich-Harris (2014-12-10 19:23:58+00:00)
Title: gh-1566

**note ready for merge**

This fixes #1566. The `addMapping()` method is sometimes called with `undefined` as the second argument - by itself that's fine (if you have `` you want to create a `bar` mapping on `` even if you don't yet know what `baz` resolves to), but it causes problems when you try to create mappings that 'leapfrog' through multiple levels. One solution is to only map one level at a time. (Dependants are still registered with the viewmodel at the top of the chain.)

However it breaks a load of other tests related to reverse mappings - I'm going to raise a separate PR about that.