Add schematic void for ignored nodes

init.lua

@@ -298,7 +298,7 @@ advschem.add_form("prob", {
 			]]
 		else
 			form = form .. [[
-				label[1,0.2;Insert item in slot.]
+				label[1,0.2;Insert node in slot.]
 			]]
 		end
 
@@ -668,7 +668,15 @@ minetest.register_on_shutdown(advschem.save)
 minetest.register_on_placenode(function(pos, newnode, player, oldnode, itemstack)
 	local smeta = itemstack:get_meta():to_table().fields
 
+	local prob
 	if smeta.advschem_prob and tonumber(smeta.advschem_prob) then
+		prob = tonumber(smeta.advschem_prob)
+	elseif newnode.name == "advschem:void" then
+		prob = 0
+	else
+		return
+	end
+
 	local px, py, pz = pos.x, pos.y, pos.z
 	for strpos, r in pairs(marked) do
 		local ap1, ap2 = r.pos1, r.pos2
@@ -683,21 +691,20 @@ minetest.register_on_placenode(function(pos, newnode, player, oldnode, itemstack
 				local prob_list = minetest.deserialize(meta:get_string("prob_list"))
 
 				local force_place = false
-					if smeta.advschem_force_place == "true" then
+				if newnode.name ~= "advschem:void" and smeta.advschem_force_place == "true" then
 					force_place = true
 				end
 
 				local ostrpos = minetest.pos_to_string(pos)
 				prob_list[ostrpos] = {
 					pos = pos,
-						prob = tonumber(smeta.advschem_prob),
+					prob = prob,
 					force_place = force_place,
 				}
 				meta:set_string("prob_list", minetest.serialize(prob_list))
 			end
 		end
 	end
-	end
 end)
 
 -- [event] Remove probability on break node
@@ -802,6 +809,17 @@ minetest.register_node("advschem:creator", {
 			advschem.show_formspec(pos, player, "prob", true)
 		end
 	end,
+	allow_metadata_inventory_put = function(pos, listname, index, stack, player)
+		if listname == "probability" then
+			local itemstring = stack:get_name()
+			if itemstring == "advschem:void" then
+				return 0
+			elseif minetest.registered_items[itemstring].type ~= "node" then
+				return 0
+			end
+		end
+		return stack:get_count()
+	end,
 	on_metadata_inventory_take = function(pos, listname, index, stack, player)
 		if listname == "probability" then
 			advschem.show_formspec(pos, player, "prob", true)
@@ -809,6 +827,23 @@ minetest.register_node("advschem:creator", {
 	end,
 })
 
+minetest.register_node("advschem:void", {
+	description = "Schematic Void",
+	tiles = { "advschem_void.png" },
+	drawtype = "nodebox",
+	is_ground_content = false,
+	paramtype = "light",
+	walkable = false,
+	sunlight_propagates = true,
+	node_box = {
+		type = "fixed",
+		fixed = {
+			{ -4/16, -4/16, -4/16, 4/16, 4/16, 4/16 },
+		},
+	},
+	groups = { dig_immediate = 3},
+})
+
 -- [entity] Display
 minetest.register_entity("advschem:display", {
 	initial_properties = {