* ClosingFuture} will be equivalent to this one.
   *
   * <p>If the function throws an exception, that exception is used as the result of the derived
   * {@code ClosingFuture}.
   *
   * <p>Example usage:
   *
   * <pre>{@code
   * ClosingFuture<List<Row>> rowsFuture =
   *     queryFuture.transform((closer, result) -> result.getRows(), executor);
   * }</pre>
   *

        @SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
        K k = (K) key;
        return function.apply(k);
      } else {
        return null;
      }
    }

    @Override
    @CheckForNull
    public V remove(@CheckForNull Object key) {
      if (backingSet().remove(key)) {
        @SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
        K k = (K) key;