@Override
    public void onFilterChange(final String text) {
        filter = text;
        if (filter != null) {
            filter = filter.trim();
            if (filter.isEmpty()) {
                filter = null;
            }
        }
        refresh();
    }
For selecting a username to add a user to a permissions set or selecting a user to add to a group.
For internal IDP this will list users from account and stroom_user combined.
For external IDP this will list users from stroom_user only and users on the IDP but not in
stroom_user will have to be manually added to the list.
stroom-core-client/src/main/java/stroom/security/client/presenter/UserRefPopupPresenter.java