Coll -- output if no index found

I am trying to figure out how to get a bang or any other type of message from [coll] if you try to retrieve data at a certain index, but it does not have any data for that index. By itself, [coll] will simply do nothing if you send it an index value for which it has no data, but I need some way of knowing that it couldn't find any data for that index. Any suggestions would be greatly appreciated!

I tried to make an example patch (below). In this example, I want it to print the stored values, or "not found" if it doesn't find any value at the queried index.