Optimise for the most common case.

Having to check for null all the time is tedious - you want to be able to just get hold of the Customer object and work with it.

In the normal case, this should work just fine - you do the look up, get the object and use it.

In the exceptional case, where you're (randomly) looking up a customer by name, not knowing whether that record/object exists, you'd need some indication that this failed. In this situation, the answer is to throw a RecordNotFound exception (or let the SQL provider beneath do this for you).

If you're in a situation where you don't know whether you can trust the data coming in (the parameter), perhaps because it was entered by a user, then you could also provide the 'TryGetCustomer(name, out customer)' pattern. Cross-reference with int.Parse and int.TryParse.