Error when generating credit invoice when I only want to return the transport refund

[jbueno]

In my Prestashop 8.1.1, I want to make a partial refund only for the carrier, not for the products. When I make the partial refund leaving the fields relating to the products empty, and I check the invoice by credit note associated with the refund made, an error appears when I try to generate the pdf.

I have checked in another Prestashop with version 1.7 and this did not happen, it seems to be a bug caused by the new version.