Include contacts that have been converted to customers (or suppliers) when "If-Modified-Since" filter is applied
When a contact is created in Xero it is not until after an invoice has been created that it gets converted to a customer (or supplier). Which is expected.
However when the "If-Modified-Since" filter is used on the GET Contacts endpoint where the "If-Modified-Since" date is after the contact is created but before the conatct as made into a supplier (i.e. after the isCustomer or isSuppler flag flips from false to true in the body of the Contact response) then the contact is not returned in the response.
I sugget a change that when a contact is converted to a supplier or a customer that the last modified date is updated so it picked up by "If-Modified-Since" filter.
Or at least document this somewhere as it's a tricky little edge case.