desc_metadata_indexer: avoid error when genre value is nil

[ndushay]

Why was this change made? 🤔

To address https://app.honeybadger.io/projects/49898/faults/87288421

While we don't want Cocina to have genres that have no value, we also don't want dor_indexing_app to blow up when it is sent them. This change will simply not try to capitalize a genre that lacks a value.

@arcadiafalcone not sure how to re-index all the affected items ...

How was this change tested? 🤨

⚡ ⚠ If this change has cross service impact, run integration tests that exercise indexing (e.g. searches in Argo for newly created/updated items, access_indexing_spec) and/or test in [stage|qa] environment, in addition to specs. ⚡

[ndushay]

tagging @arcadiafalcone to make sure she's okay wth this. Seems like a new error probably for one set of objects ...

[jcoyne]

Can you please add a test that demonstrates how this change fixes the problem?

[arcadiafalcone]

@ndushay This error is possible when creating cocina without routing through MODS first. This also relates to the conversation about requiring certain properties in validation to catch orphan attributes without a corresponding value or value-equivalent property, which would be a more comprehensive way of addressing the issue.

Slack thread from when this was done for subject: https://stanfordlib.slack.com/archives/C09M7P91R/p1659439518438329

[ndushay]

@jcoyne test added.

@arcadiafalcone I'll assume you'll make a ticket or whatever to address this problem with validation.

[ndushay]

@arcadiafalcone also assume you or someone will reindex all the affected items? (fewer than 30, I think, per honeybadger alert.)

[arcadiafalcone]

Ticket for the general issue is here: sul-dlss/cocina-models#510

[arcadiafalcone]

I've added required property lists to sul-dlss/cocina-models#510.