return t;
  }

  /** Returns {@code null} as any type, even one that does not include {@code null}. */
  @SuppressWarnings({"nullness", "TypeParameterUnusedInFormals", "ReturnMissingNullable"})
  // The warnings are legitimate. Each time we use this method, we document why.
  @ParametricNullness
  static <T extends @Nullable Object> T unsafeNull() {
    return null;
  }

  private NullnessCasts() {}

 * way to check an object at runtime to be an instance of a {@link TypeToken}. Instead, caller
 * should use the type safe {@link #putInstance}.
 *
 * <p>Also, if caller suppresses unchecked warnings and passes in an {@code Iterable<String>} for
 * type {@code Iterable<Integer>}, the map won't be able to detect and throw type error.
 *

        }
        return themeName;
    }

    /**
     * Recursively deletes a directory and all its contents.
     * Does not throw exceptions, only logs warnings if deletion fails.
     *
     * @param dir the directory to delete
     */
    protected void closeQuietly(final Path dir) {
        if (Files.notExists(dir)) {
            if (logger.isDebugEnabled()) {

     * flexibility, and debug mode warnings are enabled when debug logging is active.
     * </p>
     */
    public DataSerializer() {
        kryoThreadLocal = ThreadLocal.withInitial(() -> {
            final Kryo kryo = new Kryo();
            // TODO use kryo.register for security
            // SECURITY WARNING: setRegistrationRequired(false) allows deserialization of arbitrary classes

        if (ageMillis + minFreshMillis >= freshMillis) {
          builder.addHeader("Warning", "110 HttpURLConnection \"Response is stale\"")
        }
        val oneDayMillis = 24 * 60 * 60 * 1000L
        if (ageMillis > oneDayMillis && isFreshnessLifetimeHeuristic()) {
          builder.addHeader("Warning", "113 HttpURLConnection \"Heuristic expiration\"")
        }
        return CacheStrategy(null, builder.build())

-   [guava-discuss: For open-ended questions and discussion](https://groups.google.com/group/guava-discuss)

## IMPORTANT WARNINGS

1.  APIs marked with the `@Beta` annotation at the class or method level are
    subject to change. They can be modified in any way, or even removed, at any

   *     fetchCounterFuture, FetchException.class, x -> 0, directExecutor());
   * }
   *
   * <p>When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
   * the warnings the {@link MoreExecutors#directExecutor} documentation.
   *
   * @param input the primary input {@code Future}
   * @param exceptionType the exception type that triggers use of {@code fallback}. The exception

3. Small incremental steps
4. Don't mix with new features

### Code Quality Checklist

- [ ] Java conventions followed
- [ ] JavaDoc for public APIs
- [ ] Tests pass (`mvn test`)
- [ ] No compiler warnings
- [ ] Proper exception handling
- [ ] Resource cleanup (AutoCloseable)
- [ ] Thread-safe if needed
- [ ] Code formatted (`mvn formatter:format`)
- [ ] License headers (`mvn license:format`)

---

   * more futures or adding more {@code directExecutor()} listeners inline -- consider {@link
   * MoreExecutors#directExecutor}. Otherwise, avoid it: See the warnings on the docs for {@code
   * directExecutor}.
   *
   * <p>This is the most general listener interface. For common operations performed using

   * more futures or adding more {@code directExecutor()} listeners inline -- consider {@link
   * MoreExecutors#directExecutor}. Otherwise, avoid it: See the warnings on the docs for {@code
   * directExecutor}.
   *
   * <p>This is the most general listener interface. For common operations performed using