AP Invoices with no Item Distributions, but Accrual instead?

Hi - while doing some testing, on a 22D instance, I have raised a simple invoice, matched to a Purchase Order.

When I validated the invoice, and checked the accounting, I noticed that there are no distributions on the invoice with a LINE_TYPE_LOOKUP_CODE value of 'ITEM'. Instead, there are distributions with a LINE_TYPE_LOOKUP_CODE value of 'ACCRUAL'.

Looking on Production, I can see about 2,000 out of 30,000 invoices created for December alone meet the same condition.

I am concerned something isn't working - but I don't know what would cause an invoice to be created with no invoice distributions of Item Type, so wanted to ask here, if anyone knows?