Gracefully fail when trying to parse unknown item

init.lua

@@ -104,6 +104,11 @@ end
 
 -- Extract suitable item description for formspec
 local description_for_formspec = function(itemstring)
+	if minetest.registered_items[itemstring] == nil then
+		-- Huh? The item doesn't exist for some reason. Better give a dummy string
+		minetest.log("warning", "[doc] Unknown item detected: "..tostring(itemstring))
+		return S("Unknown item (@1)", tostring(itemstring))
+	end
 	local description = minetest.registered_items[itemstring].description
 	if description == nil or description == "" then
 		return minetest.formspec_escape(itemstring)

locale/de.txt

@@ -121,6 +121,7 @@ any level = beliebige Stufe
 level 0 = Stufe 0
 level 0-%d = Stufen 0-%d
 unknown = unbekannt
+Unknown item (@1) = Unbekannter Gegenstand (@1)
 • %s: %d = • %s: %d
 • %s: %d HP = • %s: %d TP
 • %s: %s, %s = • %s: %s, %s

locale/template.txt

@@ -121,6 +121,7 @@ any level =
 level 0 =
 level 0-%d =
 unknown =
+Unknown item (@1) =
 • %s: %d =
 • %s: %d HP =
 • %s: %s, %s =