Index: cookbook.lua
==================================================================
--- cookbook.lua
+++ cookbook.lua
@@ -526,10 +526,14 @@
 	end
 	return recipe_kinds[kind].pick(restrict), kind
 end
 
 local render_recipe = function(kind,ingredients,result,notes_right)
+	if not ingredients then
+		log.errf('tried to render %s recipe for %s but no ingredients are listed', kind, result)
+		return false
+	end
 	local k = recipe_kinds[kind]
 	local t = ''
 	local props = k.props(result)
 	for i=1,#k.slots do
 		local ing = ingredients[i]