Sanity check for null city.

src/engine/db/handlers/dbWarehouseHandler.java

@@ -136,6 +136,12 @@ public class dbWarehouseHandler extends dbHandlerBase {
                 int cityUID = rs.getInt("cityUUID");
                 JSONObject jsonObject = new JSONObject(rs.getString("warehouse"));
                 City city = City.getCity(cityUID);
+
+                if (city == null) {
+                    Logger.error("No city " + cityUID + " for warehouse");
+                    continue;
+                }
+
                 city.warehouse = new Warehouse(jsonObject);
                 city.warehouse.city = city;