Hi Luiz, were you using Authority Control for the dc.subject.cnpq field in the past?
When SolrService indexes a metadata value that is authority controlled, it tries to get the label / variant terms out of the authority index to include it in the search terms for the item.
From what I'm seeing in SolrServiceImpl, I think the problem is that the field is enabled for authority control somewhere in dspace.cfg, or the spring authority config, but there is no ChoiceAuthority plugin selected for the field.
So the service thinks it needs to try to query the authority index, since the field is configured as controlled, but doesn't know how to because the plugin (which is responsible for returning variant names, labels etc) isn't specified.
There are a few suggestions I have:
1. if you do use authority control for this field, check which plugin you'd been using previously (look in past config) and see if you can re-enable it -- it might be that it's been missing for a while in your previous instance but hadn't been a major issue if items with that field weren't being indexed or re-indexed
2. if you don't actually use authority control for this field, make sure it isn't "half-configured" in dspace.cfg, and in the (confusingly-named) orcid-authority-services.xml file.
3. if you don't use authority control but #2 doesn't work, i can see a configuration property checked in the service that isn't documented, but might help: discovery.index.authority.ignore.dc.subject.cnpq = true
This allows authority control to continue functioning but doesn't try to index any authority terms. However, you could still end up with other issues outside of indexing if you have that field enabled for authority control, but without a plugin specified, so #2 is probably better overall.
Also note, if you were using authority control in your previous instance and need to preserve those records, you'll probably need to export and import the authority index to your new server so you have the actual authority data stored with the right UUIDs. (this can be done with standard solr CSV query and update, and in new versions of DSpace can be done with the solr-statistics-export command specifying the authority core)
Cheers
Kim
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