still has pending deleted files; cannot initialize IndexWriter

[learnr27]

lockFactory=org.apache.lucene.store.NativeFSLockFactory@53b7f08 still has pending deleted files; cannot initialize IndexWriter
at org.apache.lucene.index.IndexWriter.(IndexWriter.java:789) ~[lucene-core-6.5.1.jar:6.5.1 cd1f23c63abe03ae650c75ec8ccb37762806cc75 - jimczi - 2017-04-21 12:17:15]
at dicoogle.lucene.LuceneIndexer.beginTransaction(LuceneIndexer.java:191) ~[classes/:?]
at dicoogle.lucene.LuceneIndexer.access$100(LuceneIndexer.java:49) ~[classes/:?]
at dicoogle.lucene.LuceneIndexer$2.call(LuceneIndexer.java:142) [classes/:?]
at dicoogle.lucene.LuceneIndexer$2.call(LuceneIndexer.java:132) [classes/:?]
at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266) [?:1.8.0_73]
at java.util.concurrent.FutureTask.run(FutureTask.java) [?:1.8.0_73]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_73]
at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266) [?:1.8.0_73]
at java.util.concurrent.FutureTask.run(FutureTask.java) [?:1.8.0_73]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [?:1.8.0_73]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [?:1.8.0_73]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_73]
INFO lucene.LuceneIndexer$2 (LuceneIndexer.java:174) - Finished Index Task: 1819917820,IndexReport [nIndexedFiles=0, nErrors=1, elapsedTime=3]