```
final List<String> userIds = request.getUserIds();
final List<String> keys = userIds.stream().map(p -> { 
    return removePrefix(p); 
}).collect(Collectors.toList());

```

Basically, every key in the list of `userIds` contains a prefix "\_user" which I want to remove for every key. So, I am invoking the `removePrefix` function on each item of the list and storing that result in another list called "keys"