Charge Invoice with no value entry

The NAV version is NAV 2013. I found one sales invoice that only contains one charge item, and there is no value entry associated with this sales invoice. I tried to post charge invoices without assigning to any shipment or return receipt, the system doesn't allow me to do so. Would you please let me know when a charge item can be posted without any value entry generated? May I also get your suggestion about how to fix this issue?

Thank you!