Fix TopicsImpl compile failure.
@@ -32,6 +32,9 @@ import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;
import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import javax.ws.rs.client.Entity;
