I guess this isn't surprising - but I certainly wasn't expecting it. Check out the following code snippet:

public function renderPanels(string area, any me, any group = "", any helper="") { var panels = getPanels(); if(isNull(paensl)) return; for(var i=1; i<=arrayLen(panels); i++) { if(panels[i].getArea() == arguments.area) {

Notice anything odd? How about that horrible typo on the 3rd line. But what surprised me was that this didn't throw a variable is undefined error. Since the variable didn't exist, it returned true for isNull. Obviously I expect to get nulls from my getPanels() code (a Page object may have panels) but the typo made it always return true.

Again - 100% obvious and expected - but this is the first time I've done this in CF9.