FLEX-35362 CAUSE: the DropDownController signals that the DropDownListBase is open immediately, even before the latter has actually made that change on stage. Since the opening takes one or two frames, it leaves a few milliseconds in which code which relies on that open/closed state erroneously assumes that it can use elements that should be on stage or initialized. In this case it's the layout property, which, due to the skin of the DropDownList, is only initialized once the drop down is actually open. SOLUTION: we check whether the layout is not-null, and if it is, we select items in the list as if it were closed.
NOTES: -also edited some comments, simplified Array instantiation, and removed an empty constructor. -now the unit test will pass.