Update/BulkUpdate operations should allow setting fields to null

Got a report that if you use the update/bulkUpdate operations you cannot "clear" out a field - using null.  Need to investigate this and figure out how to make this type of operation function properly.  In my mind it does make sense to not supply a field and not have it updated using this operations, however if I have a field specified and set to null that it would be set to null. 