Removing mappings generate mapping retrieval error

[jonquet]

On AGROVOC, concept "farm leases":
https://agroportal.lirmm.fr/ontologies/AGROVOC/?p=classes&conceptid=http%3A%2F%2Faims.fao.org%2Faos%2Fagrovoc%2Fc_10747&jump_to_nav=true

I just removed a duplicate mapping in the UI.
As a consequence the mapping tab does not load anymore:

[syphax-bouazzouni]

The backend is also not working https://data.agroportal.lirmm.fr/ontologies/AGROVOC/classes/http%3A%2F%2Faims.fao.org%2Faos%2Fagrovoc%2Fc_10747/mappings

[syphax-bouazzouni]

The log of the error

 NoMethodError - undefined method `process' for nil:NilClass:
        /srv/ontoportal/ontologies_api/shared/bundle/ruby/2.7.0/bundler/gems/ontologies_linked_data-e9b708c40
b2b/lib/ontologies_linked_data/mappings/mappings.rb:234:in `block in mappings_ontologies'
        /srv/ontoportal/ontologies_api/shared/bundle/ruby/2.7.0/bundler/gems/ontologies_linked_data-e9b708c40
b2b/lib/ontologies_linked_data/mappings/mappings.rb:226:in `each'
        /srv/ontoportal/ontologies_api/shared/bundle/ruby/2.7.0/bundler/gems/ontologies_linked_data-e9b708c40
b2b/lib/ontologies_linked_data/mappings/mappings.rb:226:in `mappings_ontologies'
        /srv/ontoportal/ontologies_api/shared/bundle/ruby/2.7.0/bundler/gems/ontologies_linked_data-e9b708c40
b2b/lib/ontologies_linked_data/mappings/mappings.rb:258:in `mappings_ontology'
        /srv/ontoportal/ontologies_api/releases/20230217110509/controllers/mappings_controller.rb:15:in `block in <class:MappingsController>'

[syphax-bouazzouni]

The creation and deletion of REST mappings is working for the other classes (tested with https://agroportal.lirmm.fr/ontologies/AGROVOC/?p=classes&conceptid=http%3A%2F%2Faims.fao.org%2Faos%2Fagrovoc%2Fc_50191)

[syphax-bouazzouni]

See to work now created and removed a mapping