Just reviewing this section in the documentation
How do I insert a NULL value for a field in an existing entity?
Because a save action of an existing entity will update the changed fields only, we can't use the mechanism used with saving a new entity. Instead we have to change the value of the field we want to set to NULL to a value, so it is changed, and at the same time the value should then be used to set the field to NULL. Because the properties reflecting the fields are typed, some with value types, we can't set the value typed properties to null/Nothing. Instead we use a method to do that.
Selfservicing / Adapter
// C#
CustomerEntity customer = new CustomerEntity("CHOPS");
customer.SetNewFieldValue((int)CustomerFieldIndex.ContactTitle, null);
// now save the customer. ContactTitle will become NULL.
I don't understand the point
Because the properties reflecting the fields are typed, some with value types, we can't set the value typed properties to null/Nothing
As .NET 2.0 support nullable types, why can't a null value be specified for a property?