[antlr-interest] ANTLR 3.1 incompatible change for tree parser labels?

[FranklinChen at cmu.edu]

I am upgrading from ANTLR 3.0 to 3.1, and code that I used to have in
a tree parser no longer works, because of a change to the return type
of labels:

anyWordsAndMedia
    :
        list+=anyWord+
        (
            list+=url
            list+=anyWord*
        )*
        ->
        anyWordsAndMedia(list={$list})
    ;

results in 

        List list_list=null;
        ChatWalker.anyWord_return list = null;

so that the assignment to url fails with

===
incompatible types
found   : org.talkbank.chat.antlr.ChatWalker.url_return
required: org.talkbank.chat.antlr.ChatWalker.anyWord_return
===

What is the correct way for me to do what I'd been doing up till now?

-- 
Franklin