}
        };

    // Since holder.value is 2, applying 4 should yield 6.
    assertEquals(6, adder.apply(4).intValue());

    ListenableFuture<Integer> immediateFuture = immediateFuture(4);
    Future<Integer> transformedFuture = transform(immediateFuture, adder, directExecutor());

    // The composed future also yields 6.
    assertEquals(6, getDone(transformedFuture).intValue());

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

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

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

      @ParametricNullness V value) {
    if (value == null) {
      // This cast is safe because null is assignable to V for all V (i.e. it is bivariant)
      @SuppressWarnings("unchecked")
      ListenableFuture<V> typedNull = (ListenableFuture<V>) ImmediateFuture.NULL;
      return typedNull;
    }
    return new ImmediateFuture<>(value);
  }

  /**

package com.google.common.util.concurrent;

import static com.google.common.truth.Truth.assertThat;
import static com.google.common.util.concurrent.Futures.getDone;
import static com.google.common.util.concurrent.Futures.immediateFuture;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static com.google.common.util.concurrent.Runnables.doNothing;

package com.google.common.util.concurrent;

import static com.google.common.truth.Truth.assertThat;
import static com.google.common.util.concurrent.Futures.getDone;
import static com.google.common.util.concurrent.Futures.immediateFuture;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static com.google.common.util.concurrent.Runnables.doNothing;

      ListenableFuture<V> result = callable.call();
      return checkNotNull(
          result,
          "AsyncCallable.call returned null instead of a Future. "
              + "Did you mean to return immediateFuture(null)? %s",
          callable);
    }

    @Override
    void setValue(ListenableFuture<V> value) {
      CombinedFuture.this.setFuture(value);
    }

    @Override

      checkNotNull(
          replacement,
          "AsyncFunction.apply returned null instead of a Future. "
              + "Did you mean to return immediateFuture(null)? %s",
          fallback);
      return replacement;
    }

    @Override
    void setResult(ListenableFuture<? extends V> result) {
      setFuture(result);
    }
  }

  /**

        notifyAndClearListeners();
        return;
      }

      /*
       * Almost everything in GWT is an AbstractFuture (which is as good as TrustedFuture under
       * GWT). But ImmediateFuture and UncheckedThrowingFuture aren't, so we still need this case.
       */
      try {
        forceSet(getDone(delegate));
      } catch (ExecutionException exception) {