kivy/kivy-designer — pull request #47 by kived (2014-06-13 20:58:24+00:00)
Title: handle dead proxy refs in nodetree cache

I had thought that `not wid` would handle dead references, as `wid` becomes a proxy to `NoneType`, but in fact `not wid` raises `ReferenceError`!!

````
ipdb> wid

ipdb> wid.parent_node
*** ReferenceError: weakly-referenced object no longer exists
ipdb> not wid
*** ReferenceError: weakly-referenced object no longer exists
````