SOLR re-index error - NullPointerException - SolrServiceIndexItemEditorsPlugin

[Mohana SP]

Currently migrating a DSpace 6.3 instance to DSpace 7.5. 

We've imported SOLR statistics and OAI records. 

When we run "/bin/dspace index-discovery -b" to re-index from scratch, the below error occurs. 

I've searched and removed records in the resourcepolicy table without eperson_id and epersongroup_id with the following command:  "DELETE FROM resourcepolicy where eperson_id is null and epersongroup_id is null;"

However, the same error still occurs. If you have any leads on what this error means or any pathways to a solution, it would be greatly appreciated. Thank you!

ERROR unknown unknown org.dspace.scripts.handler.impl.CommandLineDSpaceRunnableHandler @ null
java.lang.NullPointerException: null
at org.dspace.discovery.IndexingUtils.findDirectlyAuthorizedGroupAndEPersonPrefixedIds(IndexingUtils.java:111) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.SolrServiceIndexItemEditorsPlugin.additionalIndex(SolrServiceIndexItemEditorsPlugin.java:58) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.indexobject.IndexFactoryImpl.buildDocument(IndexFactoryImpl.java:67) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.indexobject.DSpaceObjectIndexFactoryImpl.buildDocument(DSpaceObjectIndexFactoryImpl.java:30) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.indexobject.ItemIndexFactoryImpl.buildDocument(ItemIndexFactoryImpl.java:143) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.indexobject.ItemIndexFactoryImpl.buildDocument(ItemIndexFactoryImpl.java:80) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.SolrServiceImpl.update(SolrServiceImpl.java:169) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.SolrServiceImpl.indexContent(SolrServiceImpl.java:159) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.SolrServiceImpl.updateIndex(SolrServiceImpl.java:344) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.SolrServiceImpl.updateIndex(SolrServiceImpl.java:331) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.SolrServiceImpl.createIndex(SolrServiceImpl.java:299) ~[dspace-api-7.5.jar:7.5]
at org.dspace.discovery.IndexClient.internalRun(IndexClient.java:72) ~[dspace-api-7.5.jar:7.5]
at org.dspace.scripts.DSpaceRunnable.run(DSpaceRunnable.java:104) [dspace-api-7.5.jar:7.5]
at org.dspace.app.launcher.ScriptLauncher.executeScript(ScriptLauncher.java:149) [dspace-api-7.5.jar:7.5]
at org.dspace.app.launcher.ScriptLauncher.handleScript(ScriptLauncher.java:131) [dspace-api-7.5.jar:7.5]
at org.dspace.app.launcher.ScriptLauncher.main(ScriptLauncher.java:98) [dspace-api-7.5.jar:7.5]