code: public Element getElementById(String id) {
          Validate.notEmpty(id);
          
          Elements elements = Collector.collect(new Evaluator.Id(id), this);
          if (elements.size() > 0)
              return elements.get(0);
          else
              return null;
      }
docs: Find an element by ID, including or under this element.
  <p>
  Note that this finds the first matching ID, starting with this element. If you search down from a different
  starting point, it is possible to find a different element by ID. For unique element by ID within a Document,
  use {@link Document#getElementById(String)}
  @param id The ID to search for.
  @return The first matching element by ID, starting with this element, or null if none found.