JS: EventTree added static nilNode to prevent some null checks
JS: EventTree added static nilNode to prevent some null checks

Signed-off-by: Matt Chudleigh <0ca390ed93f516590d05286882efa52bb3b35616@ausenco.com>
Signed-off-by: Harvey Harrison <eadbd6b462bf3c97df0300a934c12bc2e5d1fe51@ausenco.com>

jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim