ListenableFuture<? extends V>... futures) {
    ListenableFuture<List<@Nullable V>> nullable =
        new ListFuture<V>(ImmutableList.copyOf(futures), true);
    // allAsList ensures that it fills the output list with V instances.
    @SuppressWarnings("nullness")
    ListenableFuture<List<V>> nonNull = nullable;
    return nonNull;
  }

  /**

 * example, the Unicode trademark sign (™) could be confused for the letters "TM" in
 * `http://ho™ail.com`. To mitigate this, the single character (™) maps to the string (tm). There
 * is similar policy for all of the 1.1 million Unicode code points. Note that some code points such
 * as "\ud83c\udf69" are not mapped and cannot be used in a hostname.
 *
 * [Punycode](http://ietf.org/rfc/rfc3492.txt) converts a Unicode string to an ASCII string to make