Check for ndef before registering Stairs+ nodes.

stairsplus/registrations.lua

@@ -35,24 +35,26 @@ local default_nodes = { -- Default stairs/slabs/panels/microblocks:
 for _, name in pairs(default_nodes) do
 	local nodename = "default:" .. name
 	local ndef = minetest.registered_nodes[nodename]
-	local groups = {}
-	for k, v in pairs(ndef.groups)
-		-- Ignore wood and stone groups to not make them usable in crafting:
-		do if k ~= "wood" and k ~= "stone" then
-			groups[k] = v
+	if ndef then
+		local groups = {}
+		for k, v in pairs(ndef.groups)
+			-- Ignore wood and stone groups to not make them usable in crafting:
+			do if k ~= "wood" and k ~= "stone" then
+				groups[k] = v
+			end
 		end
+		local drop
+		if type(ndef.drop) == "string" then
+			drop = ndef.drop:sub(9)
+		end
+		stairsplus:register_all("moreblocks", name, nodename, {
+			description = ndef.description,
+			drop = drop,
+			groups = groups,
+			sounds = ndef.sounds,
+			tiles = ndef.tiles,
+			sunlight_propagates = true,
+		})
 	end
-	local drop
-	if type(ndef.drop) == "string" then
-		drop = ndef.drop:sub(9)
-	end
-	stairsplus:register_all("moreblocks", name, nodename, {
-		description = ndef.description,
-		drop = drop,
-		groups = groups,
-		sounds = ndef.sounds,
-		tiles = ndef.tiles,
-		sunlight_propagates = true,
-	})
 end