If you look at the function panel help for that argument it explains it. Right-click on the Address List parameter in the function panel and you will see that it says to terminate the list, there needs to be a -1. Note, this is an INPUT to the function specifying which addresses to search for listeners. This should be an array with values like 1,2,3,4,5,6,..., -1.
Best Regards,
Chris Matthews
National Instruments