Recommender throws 500 error for sample input text in the Rails application

[jvendetti]

I noticed today that the Recommender tab in production BioPortal displays a "Problem getting recommendations, please try again." error message if you click the "insert sample input" link, then click the Get Recommendations button.

The error message appears to be specific to the sample input text, i.e., if you feed that particular input text to the REST endpoint directly:

https://data.bioontology.org/recommender?input=Primary%20treatment%20of%20DCIS%20now%20includes%203%20options%3A%20lumpectomy%20without%20lymph%20node%20surgery%20plus%20whole%20breast%20radiation%20(category%201)%3B%20total%20mastectomy%20with%20or%20without%20sentinel%20node%20biopsy%20with%20or%20without%20reconstruction%20(category%202A)%3B%20lumpectomy%20without%20lymph%20node%20surgery%20without%20radiation%20(category%202B).%20Workup%20for%20patients%20with%20clinical%20stage%20l%2C%20llA%2C%20llB%2C%20or%20T3%2CN1%2CM0%20disease%20was%20reorganized%20to%20distinguish%20optional%20additional%20studies%20from%20those%20recommended%20for%20all%20of%20these%20patients.%20Recommendation%20for%20locoregional%20treatment%20for%20patients%20with%20clinical%20stage%20l%2C%20llA%2C%20llB%2C%20or%20T3%2CN1%2CM0%20disease%20with%201-3%20positive%20axillary%20nodes%20following%20total%20mastectomy%20was%20changed%20from%20%22Consider%22%20to%20%22Strongly%20consider%22%20postmastectomy%20radiation%20therapy.

... you can see the Internal Server Error displayed in a browser window. Stack trace from my local dev environment:

ArgumentError: comparison of String with 0 failed
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender/evaluators/specialization_evaluator.rb:98:in `<'
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender/evaluators/specialization_evaluator.rb:98:in `get_number_of_classes'
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender/evaluators/specialization_evaluator.rb:30:in `block in evaluate'
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender/evaluators/specialization_evaluator.rb:26:in `each'
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender/evaluators/specialization_evaluator.rb:26:in `evaluate'
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender.rb:121:in `block in get_ranking_single'
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender.rb:113:in `each'
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender.rb:113:in `get_ranking_single'
	/Users/vendetti/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/bundler/gems/ncbo_ontology_recommender-a61aa26e3535/lib/ncbo_ontology_recommender.rb:79:in `recommend'
	/Users/vendetti/Development/GitHub/ncbo/ontologies_api/controllers/recommender_controller.rb:83:in `recommend'
	/Users/vendetti/Development/GitHub/ncbo/ontologies_api/controllers/recommender_controller.rb:7:in `block (2 levels) in <class:RecommenderController>'

The 500 error isn't reproducible for the same REST call against stagedata.bioontology.org, which may indicate some kind of data corruption issue in the production environment.