docs: public void clear() {
          if (clusterMarker != null) {
              Layers mapOverlays = clusterManager.getMapView().getLayerManager().getLayers();
              if (mapOverlays.contains(clusterMarker)) {
                  mapOverlays.remove(clusterMarker);
              }
              clusterManager = null;
              clusterMarker = null;
          }
          synchronized (items) {
              items.clear();
          }
      }