code: public I run(GeneratorConsumerWithException<I> consumer) {
          try {
              consumer.accept(getThis());
          } catch (Exception e) {
              sneakyThrow(e);
          }
          return getThis();
      }
docs: Run some method. Argument is current generator,
  which allows to access current generator in run() method.
  @param consumer Consumer method which sneaks any checked exception
  https://www.baeldung.com/java-sneaky-throws
  Usage:
  SitemapIndexGenerator.of(homepage)
  .run(currentGenerator -&gt; { ... })
  .addPage(WebPage.of("test))
  .toString()
  @return this