Datetime overflow may occur when saving debtors

A SQL datetime overflow will occur when saving an existing debtor record if one of the following fields is null in table DB_Main:

• LastPurchaseDate
• LastPaymentDate
• AllocLastSavedDateTime

Whilst the debtor business logic does correctly initialise these values to not be null when a debtor is created, it is unable to cope when they are null (say from an old database upgrade or someone has updated the table directly).

The debtor business logic should check if these dates are null (date.minvalue) on save and write away DBNull.Value instead.