import static com.google.common.util.concurrent.AggregateFuture.ReleaseResourcesReason.OUTPUT_FUTURE_DONE;
import static com.google.common.util.concurrent.Futures.getDone;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static java.util.Objects.requireNonNull;
import static java.util.logging.Level.SEVERE;

import com.google.common.annotations.GwtCompatible;