[Dev-luatex] Question on node.insert_before()

Hi, this gives me an error: ---------------------------------------- \directlua{ local second=node.new("rule") local v=node.vpack(second) local first=node.new("rule") node.insert_before(v,second,first) } \bye ---------------------------------------- Attempt to node.insert_before() a non-existing node I assumed that node.insert_before would put the first node before the second node and "corrects" the list pointer of v. Q: why do I get the error? Patrick