Well, I discovered this by mistake. Here I can't make it crash doing the same with the copper layer but the code already look for photo_copper[photo_groups[1]] not being null.
At that moment setting the layer as transparent made sense to me but I don't know what is reasonable to expect. Maybe some warning message? I had a hard time before figuring out that I misplaced the layers.
Well, I discovered this by mistake. Here I can't make it crash doing the same with the copper layer but the code already look for photo_copper[ photo_groups[ 1]] not being null.
At that moment setting the layer as transparent made sense to me but I don't know what is reasonable to expect. Maybe some warning message? I had a hard time before figuring out that I misplaced the layers.