code: Marker addMarker() {
      if (!lazyInitDocumentation()) {
        return null;
      }
  
      if (documentation.markers == null) {
        documentation.markers = new ArrayList<>();
      }
  
      Marker marker = new Marker();
      documentation.markers.add(marker);
      return marker;
    }
docs: Adds a marker to the documentation (if it exists) and
  returns the marker. Returns null otherwise.