Overview:
Steps to Reproduce:

1. Using the [Patron API|https://s3.amazonaws.com/foliodocs/api/edge-patron/p/edge-patron.html#patron_account_idinstanceinstanceid_hold_post,] create a Title-level request for an Instance with a Holding, but with no Items attached

1. Using the same API, cancel the request.

Expected Results:

The request is cancelled:

Actual Results:

Additional Information:
Adding an item after the request was created also renders HTTP 500. If there is an item at the time for the request, the API works as expected.
This HTTP 500 in mod-patron makes the edge-patron call also raise a HTTP 500, which makes the Discovery user experience hard to handle.
Interested parties:

All libraries with a discovery tool/OPAC that allows you to make TLRs on things without Items, All libraries wanting to post requests for things without holdings. Not an uncommon practice when you want to order specific issues of journals. Not sure how common it is for FOLIO libraries. Having Instances without Items is very common though.

Verified in both live Morning Glory environments and in Nolana.