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...