* 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
   *     type is matched against the input's exception. "The input's exception" means the cause of
   *     the {@link ExecutionException} thrown by {@code input.get()} or, if {@code get()} throws a

   * 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
   *     type is matched against the input's exception. "The input's exception" means the cause of
   *     the {@link ExecutionException} thrown by {@code input.get()} or, if {@code get()} throws a