It is supposed to report the WatcherMorph which is asked for (in this case, the watcher named "name"), not nothing.
I think you may have to do this.parentThatIsA(IDE_Morph) in order to get it to work.
As far as I'm aware, IDE_Morph does not contain the findVariableWatcher method.
The 
itself iterates over stage.children to find an instance of the WatcheMorph so it seems that there is no such method.
BTW: It's definitely not a Snap! bug report...