Email field - Alternate recipient address

In the Business mapping of EDS, we have the option of defining our business partner with recipient e-mail (e-mail field), language code, etc. On the respective card such as customer/vendor/business partner, there is only one e-mail field in the standard. More and more, we are adding more and more email fields in each project at the level of the master data card. In business mapping, for example, we define the use of the e-mail field "e-mail invoice" when sending invoices.
What if this is not filled? Sure... was now, the EDS will tell that the value "empty" is invalid and thus the sending fails.
Better I would feel that you have such a "case definition".
Means that an alternative e-mail field is used, such as the standard e-mail field that exists on the customer/vendor/business partner card. This would ensure, in the event that the e-mail field "Invoices" is empty, that the standard e-mail address is sent.