Always provide a default case for switch

src/ol/source/imagesource.js

@@ -178,6 +178,8 @@ ol.source.Image.prototype.handleImageChange = function(event) {
           new ol.source.ImageEvent(ol.source.ImageEventType.IMAGELOADERROR,
               image));
       break;
+    default:
+      // pass
   }
 };
 

src/ol/source/urltilesource.js

@@ -143,6 +143,8 @@ ol.source.UrlTile.prototype.handleTileChange = function(event) {
       this.dispatchEvent(
           new ol.source.TileEvent(ol.source.TileEventType.TILELOADERROR, tile));
       break;
+    default:
+      // pass
   }
 };