Harvesting : message "javax.ejb.EJBTransactionRolledbackException, Exception thrown from bean: java.lang.NullPointerException"

Hi
I'm going on here with other harvesting problems from Dataverse 5.2. I'm opening another issue, the behaviour and messages obtained being different.
I get the message
javax.ejb.EJBTransactionRolledbackException, Exception thrown from bean: java.lang.NullPointerException
for every record from these two repositories :

• https://www.ortolang.fr/ : 0 record harvested on 1 available. An example of record can be found here : https://repository.ortolang.fr/api/oai?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai:ortolang.fr:3a31c6b2-8536-41e7-90a8-788474546269
• https://ordar.otelo.univ-lorraine.fr : 0 records harvested on 27 available
  I still think this could be a misconfiguration on our Dataverse but I need help here.

Regarding Ortolang, a look at the XML record shows three entries for dc:identifier (I checked this after having read https://github.com/IQSS/dataverse/issues/7497) ; they're however the same and the first one is valid. It's a handle, which I believe Dataverse should manage?

Here are the client configurations :

Alias : ordar_test
Server URL : https://ordar.otelo.univ-lorraine.fr/oai
Local dataverse : moissonnage_ordar_test
OAI set : HYDROLOGY
Metadata format : oai_dc
Repository type : Generic OAI archive

Alias :ortolang_test
Server URL :http://repository.ortolang.fr/api/oai
Local dataverse : 
OAI set : a73bcbad-4c94-47f0-97e3-08c9846d791d
Metadata format : oai_dc
Repository type : Generic OAI archive

These two repositories both present oai_dc and oai_datacite metadata. If I try the latter I get the message
Exception processing getRecord(), oaiUrl=https://ordar.otelo.univ-lorraine.fr/oai, identifier=info:doi:10.24396/ORDAR-56, edu.harvard.iq.dataverse.api.imports.ImportException, Unsupported import metadata format: oai_datacite.

Here are the logs for the attempts in the oai_dc format :
harvest_ortolang_test_2021-01-27T10-06-53.log.gz
harvest_ordar_test_2021-01-27T09-32-46.log.gz

Again, thanks in advance for your time or any insight.

Best
Thomas

EDIT : DV version changed (5.2 and not 5.3)