I am currently working on migrating a project from an old version of Solr to Elasticsearch, and came across a funny (to me at least) difference in the "default" behavior of JapanesePartOfSpeechStopFilterFactory.
If JapanesePartOfSpeechStopFilterFactory is given empty args, it does nothing. It doesn't load any stop tags, and just passes along the TokenStream passed to create(). (By comparison, the Elasticsearch filter will default to loading the stop tags shipped in the Kuromoji analyzer JAR.) So, for many years, my project was not using JapanesePartOfSpeechStopFilter, when I thought that it was. I would like to create an issue and submit a patch, in case other users out there are failing to use the filter factory correctly, but I'm not sure what the best approach is, between: 1. If someone doesn't specify the tags argument, then throw an exception (because the user probably doesn't know what they're doing). 2. If someone doesn't specify the tags argument, then load the default stop tags (like JapaneseAnalyzer does). I would lean more toward 1, to avoid a silent change in behavior.
