code: public <T> I addPageNames(Collection<T> webPages, Function<T, String> mapper) {
          for (T element : webPages) {
              addPage(WebPage.of(mapper.apply(element)));
          }
          return getThis();
      }
docs: Add collection of pages to sitemap
  
  @param <T> This is the type parameter
  @param webPages Collection of pages
  @param mapper Mapper function which transforms some object to String. This will be passed to WebPage.of(name)
  @return this