* java.util.stream}), which is similar to {@code FluentIterable} but generally more powerful. Key
 * differences include:
 *
 * <ul>
 *   <li>A stream is <i>single-use</i>; it becomes invalid as soon as any "terminal operation" such
 *       as {@code findFirst()} or {@code iterator()} is invoked. (Even though {@code Stream}
 *       contains all the right method <i>signatures</i> to implement {@link Iterable}, it does not

 *       Future} returned by this class, the next task may still have to wait.</i>.
 *   <li>Once an {@code AsyncCallable} returns a {@code Future}, this class considers that task to
 *       be "done" as soon as <i>that</i> {@code Future} completes in any way. Notably, a {@code
 *       Future} is "completed" even if it is cancelled while its underlying work continues on a

     *
     * <p>Prefer the equivalent method {@link #buildOrThrow()} to make it explicit that the method
     * will throw an exception if there are duplicate keys. The {@code build()} method will soon be
     * deprecated.
     *
     * @throws IllegalArgumentException if duplicate keys were added
     */
    public ImmutableMap<K, V> build() {
      return buildOrThrow();
    }

    /**

        // effective model.
        //
        // As of 3.4, the model version is mandatory even in raw models. The XML element still is optional in the
        // XML schema and this will not change anytime soon. We do not want to build effective models based on
        // models without a version starting with 3.4.
        validateStringNotEmpty("modelVersion", problems, Severity.ERROR, Version.V20, m.getModelVersion(), m);