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https://issues.apache.org/jira/browse/OPENNLP-238?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13073008#comment-13073008
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Jörn Kottmann commented on OPENNLP-238:
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Ups, we should fix the typo in this error message.
That explains your issue, the tag dictionary denies all sequences beam search
could advance, therefore it can only return null which is causing the NPE you
see.
Why isn't cross validation not checking the dictionary, does it not support it?
> BestSequence method in BeamSearch can cause NullPointerException if it can
> not find a valid sequence
> ----------------------------------------------------------------------------------------------------
>
> Key: OPENNLP-238
> URL: https://issues.apache.org/jira/browse/OPENNLP-238
> Project: OpenNLP
> Issue Type: Bug
> Components: POS Tagger
> Affects Versions: tools-1.5.2-incubating
> Reporter: William Colen
> Assignee: William Colen
> Fix For: tools-1.5.2-incubating
>
>
> I am using the standard sequence validator of POS Tagger with a
> TagDictionary. Sometimes there are no outcome that matches with the tags in
> the dictionary. That is causing a NullPointerException in bestSequence method.
> I think we should add an extra validation: if the heap 'next' still empty
> after advancing all valid sequences (line 159) we should let it advance
> invalid sequences. It would make the POS Tagger more robust.
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