Fix

DoubleDeckerBus/DoubleDeckerBus/DrawingObjectBus.cs

@@ -56,5 +56,10 @@ namespace DoubleDeckerBus
         {
             return new DrawingObjectBus(data.CreateDrawningCar());
         }
+
+        public DrawingBus getBus()
+        {
+            return _bus;
+        }
     }
 }

DoubleDeckerBus/DoubleDeckerBus/SetBusesGeneric.cs

@@ -31,7 +31,7 @@ namespace DoubleDeckerBus
         {
             try
             {
-                if (bus.getBus(bus.Get_bus()) == null)
+                if (bus.getBus() == null)
                 {
                     throw new NullReferenceException();
                 }