Concurrent Modification Exception for SOLR indexing

2019-02-03 15:40:11,653 [XWiki initialization] INFO  .HibernateDataMigrationManager - Data migration [R1100000XWIKI15620] applied successfully, database [xwiki] upgraded to version [1100000]
2019-02-03 15:40:59,782 [XWiki Solr index thread] ERROR o.x.s.s.i.DefaultSolrIndexer   - Failed to process entry [INDEX xwiki:XWiki.Admin]
org.xwiki.search.solr.internal.api.SolrIndexerException: Failed to get input Solr document for entity 'xwiki:XWiki.Admin'
        at org.xwiki.search.solr.internal.metadata.AbstractSolrMetadataExtractor.getSolrDocument(AbstractSolrMetadataExtractor.java:140)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.getSolrDocument(DefaultSolrIndexer.java:504)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.processBatch(DefaultSolrIndexer.java:411)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.run(DefaultSolrIndexer.java:377)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.util.ConcurrentModificationException: null
        at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
        at java.util.ArrayList$Itr.next(ArrayList.java:851)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setObjects(DocumentSolrMetadataExtractor.java:199)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setExtras(DocumentSolrMetadataExtractor.java:186)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setFieldsInternal(DocumentSolrMetadataExtractor.java:135)
        at org.xwiki.search.solr.internal.metadata.AbstractSolrMetadataExtractor.getSolrDocument(AbstractSolrMetadataExtractor.java:133)
        ... 4 common frames omitted
2019-02-03 15:41:10,340 [XWiki Solr index thread] ERROR o.x.s.s.i.DefaultSolrIndexer   - Failed to process entry [INDEX xwiki:XWiki.Admin]
org.xwiki.search.solr.internal.api.SolrIndexerException: Failed to get input Solr document for entity 'xwiki:XWiki.Admin'
        at org.xwiki.search.solr.internal.metadata.AbstractSolrMetadataExtractor.getSolrDocument(AbstractSolrMetadataExtractor.java:140)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.getSolrDocument(DefaultSolrIndexer.java:504)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.processBatch(DefaultSolrIndexer.java:411)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.run(DefaultSolrIndexer.java:377)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.util.ConcurrentModificationException: null
        at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
        at java.util.ArrayList$Itr.next(ArrayList.java:851)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setObjects(DocumentSolrMetadataExtractor.java:199)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setExtras(DocumentSolrMetadataExtractor.java:186)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setFieldsInternal(DocumentSolrMetadataExtractor.java:135)
        at org.xwiki.search.solr.internal.metadata.AbstractSolrMetadataExtractor.getSolrDocument(AbstractSolrMetadataExtractor.java:133)
        ... 4 common frames omitted
2019-02-03 15:41:37,153 [XWiki Solr index thread] ERROR o.x.s.s.i.DefaultSolrIndexer   - Failed to process entry [INDEX xwiki:XWiki.Admin]
org.xwiki.search.solr.internal.api.SolrIndexerException: Failed to get input Solr document for entity 'xwiki:XWiki.Admin'
        at org.xwiki.search.solr.internal.metadata.AbstractSolrMetadataExtractor.getSolrDocument(AbstractSolrMetadataExtractor.java:140)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.getSolrDocument(DefaultSolrIndexer.java:504)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.processBatch(DefaultSolrIndexer.java:411)
        at org.xwiki.search.solr.internal.DefaultSolrIndexer.run(DefaultSolrIndexer.java:377)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.util.ConcurrentModificationException: null
        at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
        at java.util.ArrayList$Itr.next(ArrayList.java:851)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setObjects(DocumentSolrMetadataExtractor.java:199)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setExtras(DocumentSolrMetadataExtractor.java:186)
        at org.xwiki.search.solr.internal.metadata.DocumentSolrMetadataExtractor.setFieldsInternal(DocumentSolrMetadataExtractor.java:135)
        at org.xwiki.search.solr.internal.metadata.AbstractSolrMetadataExtractor.getSolrDocument(AbstractSolrMetadataExtractor.java:133)
        ... 4 common frames omitted
2019-02-03 15:45:00.060:INFO:oxtjl.NotifyListener:Thread-1: ----------------------------------
2019-02-03 15:45:00.060:INFO:oxtjl.NotifyListener:Thread-1: Server stopping, please wait while all resources are closed...
2019-02-03 15:45:00.066:INFO:oejs.AbstractConnector:Thread-1: Stopped ServerConnector@c67a89{HTTP/1.1,[http/1.1]}{0.0.0.0:8080}