with a void dimension, giving it either a liquid or material results in a warning. It does accept them and build properly if you ignore the warning.

Not specifying results in them being randomly chosen.

Personally, it makes sense to me that it shouldn't take nor generate a liquid or material.

Running FTB Infinity Evolved 2.3.5

I don't understand. In a void world there is no material or liquid to generate so what's the problem exactly? The warning is specifically to tell you that it doesn't make sense to add a material or liquid

Because it will random generate them if you don't supply one, which you will then have to pay the maintenance cost for even though nothing actually gets spawned.

That wasn't terribly clear:

It warns you, even though it does accept the modifiers. If you don't supply modifiers, it selects them randomly. Which wouldn't be a big deal, until it randomly select diamond ore and you're paying tens of thousands of extra rf for no reason.

So the warning doesn't really make sense with how it currently acts. If it didn't take a liquid or material, and didn't generate one, that would make more sense, and the warning would make sense.

Ah right

From now on if you don't specify and material or liquid for 'void' it will always randomly generate stone and water to prevent undesired bad costs, So material default and liquid default are not needed. This will be in next version (both 1.7.10 and 1.8.9)