code: private WmsLayer getLayer(String layerId) {
  		RasterLayer layer = configurationService.getRasterLayer(layerId);
  		if (layer instanceof WmsLayer) {
  			return (WmsLayer) layer;
  		}
  		return null;
  	}
docs: Given a layer ID, search for the WMS layer.
  
  @param layerId layer id
  @return WMS layer or null if layer is not a WMS layer