Extension method instead of Null Object pattern

Question

I'm wondering to using extension method to avoid checking for null in hierarchy. The example:

// GetItems(), GetFirstOrDefault(), GetProduct(), GetIDProduct() are extension methods like:
public static SomeType GetSomeProperty( this XYZ obj ) {
    if ( object.ReferenceEquals( obj, null ) ) { return default( SomeType ); }
    return obj.SomeProperty;
}

// the code with extension methods
Guid? idProduct = this.Invoice.GetItems().GetFirstOrDefault().GetProduct().GetIDProduct();
// instead of
Guid? idProduct = null;
Invoice invoice = this.Invoce;
if ( null != invoice ) {
    InvoiceItems items = invoice.Items;
    if ( null != items && items.Count > 0 ) {
        InvoiceItem item = items[0];
        if ( null != item ) {
            idProduct = item.IDProduct();
        }
    }
}

I know, there is available Null Object pattern, but the solution with this type of extension methods looks better.

Do you think, this solution is good or bad (because bad/good design, lucidity, whatever else)?

Please vote "Good" or "Bad" and why do you think so. Posts are flaged as community.

Answer 1

Please vote this for "good solution".

Answer 2

Please vote this for "bad solution".

Answer 3

I'd just do it sanely:

Guid? idProduct = null;
Invoice invoice = this.Invoce;

if (invoice != null && 
    invoice.Items != null &&
    invoice.Items.Count > 0 &&
    invoice.Items[0] != null) 
{
   idProduct = invoice.Items[0].IDProduct();
}

Answer 4

This breaks the semantics of an instance method. Extension methods look like instance methods to the callers, and as such should behave like them. When you break semantics like this, the code will be harder to understand and maintain, its behavior will surprise most developers.

Answer 5

I vote this as "not-interested-in-that-solution".

I'm fine with a Null-Object-Pattern for my entity model classes.