yes it is new, it's a crown store item than can replace any style matérial (where my confusion on the error came from at first)
it's a checkbox. a new one that will come with Thieves Guild

Edit: I wrote "hook" in the post title, but this control name is so long, no eye can reach there


here how it was before (source : wiki of last summer) :
## SetPendingSmithingItem(luaindex patternIndex, luaindex materialIndex, integer materialQuantity, luaindex styleIndex, luaindex traitIndex)

so yes i was passing nil, but now if i display the args I got : index,index,index,index,index,bool,nil ... haven't checked the updated function yet. obviously the bool is for isUsingUniversalStyle, but the nil?