@SafeVarargs
  public static <V extends @Nullable Object> ListenableFuture<List<V>> allAsList(
      ListenableFuture<? extends V>... futures) {
    ListenableFuture<List<@Nullable V>> nullable =
        new ListFuture<V>(ImmutableList.copyOf(futures), true);
    // allAsList ensures that it fills the output list with V instances.
    @SuppressWarnings("nullness")
    ListenableFuture<List<V>> nonNull = nullable;
    return nonNull;
  }

import com.google.common.testing.TestLogHandler;
import com.google.common.util.concurrent.Callables;
import com.google.common.util.concurrent.ExecutionError;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.UncheckedExecutionException;
import java.io.IOException;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

                  @Override
                  public String call(DeferredCloser closer) throws Exception {
                    return "value";
                  }
                }),
            executor);
    ListenableFuture<?> statusFuture = closingFuture.statusFuture();
    waiter.awaitStarted();
    assertThat(statusFuture.isDone()).isFalse();
    waiter.awaitReturned();
    assertThat(getUninterruptibly(statusFuture)).isNull();
  }

 * AsyncCacheLoader.asyncLoad}</a> must return a {@code CompletableFuture}. Users of Guava's {@link
 * com.google.common.util.concurrent.ListenableFuture} can adapt between the two {@code Future}
 * types by using <a href="https://github.com/lukas-krecan/future-converter#java8-guava">{@code
 * net.javacrumbs.futureconverter.java8guava.FutureConverter}</a>.
 *