How to composite exr without alpha?

cgidesign

I have a set of exr render passes (e.g. diffuse, volume, glossy). They are render LPEs out of DS.
Those exrs don’t have a transparent background - instead where there is no data they are just black.

All the Blender tutorials I found, use the alpha over node to composite. But how to do it when there is no alpha?

In a 32bit capable image editing software I can use the “add blend mode” to recreate the beauty pass, but how to do it in Blender?

cgidesign

Nevermind; found out that Color Mix set to add does the trick.