Better way to catch that incoming nil, return a real value on the way out

autoplace_tubes.lua

@@ -28,6 +28,8 @@ end
 
 --a function for determining which side of the node we are on
 local function nodeside(node, tubedir)
+	if not tubedir or not node or not node.param2 then return "back" end
+
     --get a vector pointing back
     local backdir = minetest.facedir_to_dir(node.param2)