*/
public List<String> execute() throws RiakException {
if (value == null && (to == null || from == null)) {
throw new IllegalStateException("Must set either value or range");
}
final IndexQuery indexQuery = makeIndexQuery();
List<String> keys = retrier.attempt(new Callable<List<String>>() {
public List<String> call() throws Exception {
return client.fetchIndex(indexQuery);
}