Highlighting: String index out of range

gistfile1.java

org.elasticsearch.search.fetch.FetchPhaseExecutionException: [myindex][0]: query[filtered(code.code.ngram:sam code.code.ngram:xy)->cache(_type:product)],from[0],size[10]: Fetch Failed [Failed to highlight field [code.ngram]]
  at org.elasticsearch.search.highlight.HighlightPhase.hitExecute(HighlightPhase.java:335)
	at org.elasticsearch.search.fetch.FetchPhase.execute(FetchPhase.java:250)
	at org.elasticsearch.search.SearchService.executeFetchPhase(SearchService.java:326)
	at org.elasticsearch.search.action.SearchServiceTransportAction.sendExecuteFetch(SearchServiceTransportAction.java:243)
	at org.elasticsearch.action.search.type.TransportSearchQueryAndFetchAction$AsyncAction.sendExecuteFirstPhase(TransportSearchQueryAndFetchAction.java:75)
	at org.elasticsearch.action.search.type.TransportSearchTypeAction$BaseAsyncAction.performFirstPhase(TransportSearchTypeAction.java:205)
	at org.elasticsearch.action.search.type.TransportSearchTypeAction$BaseAsyncAction.performFirstPhase(TransportSearchTypeAction.java:192)
	at org.elasticsearch.action.search.type.TransportSearchTypeAction$BaseAsyncAction$2.run(TransportSearchTypeAction.java:178)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
	at java.lang.Thread.run(Thread.java:680)
Caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: -14
	at java.lang.String.substring(String.java:1937)
	at org.apache.lucene.search.vectorhighlight.BaseFragmentsBuilder.makeFragment(BaseFragmentsBuilder.java:166)
	at org.apache.lucene.search.vectorhighlight.AbstractFragmentsBuilder.createFragments(AbstractFragmentsBuilder.java:84)
	at org.apache.lucene.search.vectorhighlight.FastVectorHighlighter.getBestFragments(FastVectorHighlighter.java:186)
	at org.elasticsearch.search.highlight.HighlightPhase.hitExecute(HighlightPhase.java:327)
	... 10 more