1) effect allows NULL to be passed for last vector effect_layer requires a vector. Not sure which is correct but they are different.

2) in some cases effect_layer will not render particles unless there is a panel created. Panel does not need to be visible. I have code that shows this but it it several thousand lines. In short test programs effect_layer works without a panel. The particle functions are being called in both cases (with/without panel) but are not rendering.