import static com.google.common.util.concurrent.Futures.immediateFailedFuture;
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.ReflectionFreeAssertThrows.assertThrows;

import com.google.common.annotations.GwtCompatible;
import java.util.concurrent.CancellationException;

    TestCallable secondCallable = new TestCallable(immediateVoidFuture());
    ListenableFuture<@Nullable Void> secondFuture =
        serializer.submitAsync(secondCallable, directExecutor());
    TestCallable thirdCallable = new TestCallable(immediateVoidFuture());
    @SuppressWarnings({"unused", "nullness"})

    // oldFuture completes.
    Runnable listener =
        () -> {
          if (taskFuture.isDone()) {
            // Since the value of oldFuture can only ever be immediateVoidFuture() or setFuture of a
            // future that eventually came from immediateVoidFuture(), this doesn't leak throwables
            // or completion values.
            newFuture.setFuture(oldFuture);

    // oldFuture completes.
    Runnable listener =
        () -> {
          if (taskFuture.isDone()) {
            // Since the value of oldFuture can only ever be immediateVoidFuture() or setFuture of a
            // future that eventually came from immediateVoidFuture(), this doesn't leak throwables
            // or completion values.
            newFuture.setFuture(oldFuture);

   * 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.
   *