"Region cannot be empty" error, what does this mean??

I've been dabbling in some region 3 stuff this morning, and I ran across an issue with the following code:

local module = {}

function module:Explode(pos, size)
	local region = Region3.new(pos, size)
	local partsInRegion = workspace:FindPartsInRegion3(region)
	
	for i, part in pairs(partsInRegion) do
		AddVelocity(part)
	end
	
	local expandedRegion = region:ExpandToGrid(4)
	
	workspace.Terrain:ReplaceMaterial(expandedRegion, 4, Enum.Material.Air, Enum.Material.Ground)
end

return module

Note: this is in a ModuleScript, and the function AddVelocity is hidden.

The error says says Region cannot be empty. If you would like to know the pos and size values, pos is generated by a script, and size is Vector3.new(8,8,8). The pos can be anywhere between -448 and 448 on the x and z axis, and -20 on the y axis.