Null handling for clurster / marker etc. items

[radzio]

@BindingAdapter("gmv_clusterItems")
  public static <T> void clusterItems(GoogleMapView googleMapView,
      Collection<T> items) {
    if (items == null) {
      return;
    }

    googleMapView.clusterItems(items);
  }

We should handle nulls differently. If user passes null IMHO we should remove all elements.