500 error when numeric field and FieldFeatureStoredValueExtractorFactory

[hiroki23]

ltr_features.conf

{
      "name": "test_f",
      "class": "org.nlp4l.solr.ltr.FieldFeatureStoredValueExtractorFactory",
      "params": { "field": "test_f" }
    }

then

/features?command=download&procId=procId

returns 500 error.

error message:

Reader: 8: List should have ] or a first element after the open [, instead had token: end of file (if you want end of file to be part of a string value, then double-quote it)

https://gist.githubusercontent.com/hiroki23/84a535c5d7b2aeb6797cfb515381bd53/raw/7340bb768f7916e71142e9d4485274cbbe3b0a9b/error.json

"field": "test_s" is OK.