From 92d7c464842e9b3619ca03bdede514ae783f9fe8 Mon Sep 17 00:00:00 2001
From: Alexander Weber <web.alexander@web.de>
Date: Fri, 16 Dec 2016 13:47:35 +0100
Subject: [PATCH] be sure recipe_def.groups is provided

---
 api.lua | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/api.lua b/api.lua
index 31fb73b..d288a95 100644
--- a/api.lua
+++ b/api.lua
@@ -49,10 +49,11 @@ function carpets.register(recipe, def)
 	if not node.groups then
 		node.groups = {}
 		-- copy by value because of some changes
-		for k, v in pairs(recipe_def.groups) do
-			node.groups[k] = v
+		if recipe_def.groups then
+			for k, v in pairs(recipe_def.groups) do
+				node.groups[k] = v
+			end
 		end
-
 		node.groups.leafdecay = nil
 	end