Upgrade SOLR 6.0 to 8.9

Solution for Upgrade SOLR 6.0 to 8.9
is Given Below:

I am trying to hopscotch the SOLR from the 6th version to the 8th version (6.0.0 -> 8.9.0)

The thing is: I want to avoid reindexing the CORS, so I backed up the CORS folders “/conf” and “/data” and after the upgrade, I replaced the folders to have the previous data. It worked fine from SOLR 7 to 8.

But from version 6.0.0 to 8.9.0 I am receiving the following error:

Caused by: org.apache.solr.client.solrj.impl.HttpSolrClient$RemoteSolrException: Error from server at http://localhost:8983/solr/{core-example}: SolrCore '{core-example}' is not available due to init failure: Error opening new searcher
        at org.apache.solr.client.solrj.impl.HttpSolrClient.executeMethod(HttpSolrClient.java:575)
        at org.apache.solr.client.solrj.impl.HttpSolrClient.request(HttpSolrClient.java:241)
        at org.apache.solr.client.solrj.impl.HttpSolrClient.request(HttpSolrClient.java:230)
        at org.apache.solr.client.solrj.SolrRequest.process(SolrRequest.java:150)
        at org.apache.solr.client.solrj.SolrRequest.process(SolrRequest.java:167)
        at com.e7solutions.solr.indexer.fields.FieldsUtil.getNames(FieldsUtil.java:100)
        at com.e7solutions.solr.indexer.indexers.TypeIndexer.loadExistingFields(TypeIndexer.java:319)
        at com.e7solutions.solr.indexer.indexers.TypeIndexer.addNewFieldsToSolr(TypeIndexer.java:252)
        at com.e7solutions.solr.indexer.indexers.TypeIndexer.indexPrimaryAttributes(TypeIndexer.java:171)
        at com.e7solutions.solr.indexer.indexers.TypeIndexer.index(TypeIndexer.java:119)
        at com.e7solutions.solr.indexer.indexers.MedicalIndexer.index(MedicalIndexer.java:158)
        at com.e7solutions.solr.indexer.SolrIndexer.main(SolrIndexer.java:86)   

Do you guys have any insights about this?

Thank you so much in advance.