I reported a bug on apollocoder and Mike Chamber forwarded it to their QA team :) :) :)

Anyways, The bug is :
Using ScreenMouseEvent.CLICK , something like :
SystemTrayIcon(Shell.shell.icon).addEventListener(ScreenMouseEvent.CLICK,showScreen)
Gives error:
TypeError: Error #2007: Parameter type must be non-null.
Work arround, Hardcode the "click" string as :
SystemTrayIcon(Shell.shell.icon).addEventListener("click",showScreen)
The problem does not occur in :
ScreenMouseEvent.RIGHT_CLICK
ScreenMouseEvent.RIGHT_MOUSE_DOWN
ScreenMouseEvent.RIGHT_MOUSE_UP