import static com.google.common.util.concurrent.ClassPathUtil.parseJavaClassPath;
import static com.google.common.util.concurrent.Futures.getChecked;
import static com.google.common.util.concurrent.Futures.immediateFuture;
import static com.google.common.util.concurrent.FuturesGetCheckedInputs.CHECKED_EXCEPTION;
import static com.google.common.util.concurrent.FuturesGetCheckedInputs.ERROR;

    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);

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.ReflectionFreeAssertThrows.assertThrows;

import static com.google.common.util.concurrent.Futures.immediateCancelledFuture;
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.MoreExecutors.directExecutor;
import static com.google.common.util.concurrent.SneakyThrows.sneakyThrow;
import static java.util.concurrent.Executors.callable;

      ListenableFuture<? extends O> output = function.apply(input);
      checkNotNull(
          output,
          "AsyncFunction.apply returned null instead of a Future. "
              + "Did you mean to return immediateFuture(null)? %s",
          function);
      return output;
    }

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

  /**

   * // counters.
   * ListenableFuture<Integer> faultTolerantFuture =
   *     fetchCounters().catchingAsync(
   *         FetchException.class, x -> immediateFuture(0), directExecutor());
   * }
   *
   * <p>The fallback can also choose to propagate the original exception when desired:
   *
   * {@snippet :

import static com.google.common.util.concurrent.Futures.immediateCancelledFuture;
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.MoreExecutors.directExecutor;
import static com.google.common.util.concurrent.SneakyThrows.sneakyThrow;
import static java.util.concurrent.Executors.callable;

      ListenableFuture<? extends O> output = function.apply(input);
      checkNotNull(
          output,
          "AsyncFunction.apply returned null instead of a Future. "
              + "Did you mean to return immediateFuture(null)? %s",
          function);
      return output;
    }

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

  /**