[Extension()]
public static bool IsNullEntity( 
   EntityAspect entity
)

// Sample showing IsNullEntity check.

    DomainModelEntityManager mgr = new DomainModelEntityManager();

    // Try to retrieve order #1 - FirstOrNullEntity will return null entity if not found.
    OrderSummary order = mgr.OrderSummaries.FirstOrNullEntity(o => o.Id == 1);
    if (order.IsNullEntity)
       Console.WriteLine("Order #1 not found");

    // Now try another order, using FirstOrDefault, which returns null if not found.
    OrderSummary order2 = mgr.OrderSummaries.FirstOrDefault(o => o.Id == 2);
    if (order2 == null) {
       Console.WriteLine("Order #2 is null");
    } else if (order2.IsNullEntity) {
       Console.WriteLine("Order #2 is a null entity");
    }

    // Note, you can't use .First (since the EF will throw an exception).
    OrderSummary order3 = mgr.OrderSummaries.First(o => o.Id == 3);