The TypeaheadCompositeSource's member "results" of is by default and does not gets initialized until the method #didChange is called.
This diff fix the logic that checks the length of "results" which can still be null.
Fix the issue that non-result node may be chosen.
Allow non-result node to be displayed with the result nodes.
Fix Typeahead (regression introduced by commit c59b8ba)
Fix JS error from TypeaheadCompositeSource.
The callback function childWaiting checks the length of this.result which could
be null and cause JS error.