import static com.google.common.util.concurrent.Futures.immediateCancelledFuture;
import static com.google.common.util.concurrent.Futures.immediateFuture;
import static com.google.common.util.concurrent.Futures.immediateVoidFuture;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static java.util.Objects.requireNonNull;

import com.google.common.annotations.GwtIncompatible;

   * immediateFuture(null)} except that it is restricted to produce futures of type {@code Void}.
   *
   * @since 29.0
   */
  @SuppressWarnings("unchecked")
  public static ListenableFuture<@Nullable Void> immediateVoidFuture() {
    return (ListenableFuture<@Nullable Void>) ImmediateFuture.NULL;
  }

  /**
   * Returns a {@code ListenableFuture} which has an exception set immediately upon construction.
   *