Using paramset with multi-valued keys leads to a 500

Here's my use case:
I wanted to use param-sets to have facet.field=field1&facet.field=field2
For the same, here is what I updated:

curl http://localhost:8983/solr/bike/config/params -H 'Content-type:application/json' -d 
'{
  "set" : { 
    "facets" : {
      "facet.field":["start_station_name","end_station_name"]
    }
  }
}'

When I tried to use the same, I got a 500.

After looking at the code, seems like, RequestParams uses MapSolrParams, which banks on Map<String,String> map.

This would need to change to support the multi-values.

I also tried sending:

solr-5.0.0-SNAPSHOT > curl http://localhost:8983/solr/bike/config/params -H 'Content-type:application/json' -d '{"update" : { "facets" : {"facet.field":"start_station_name","facet.field":"end_station_name"}}}'

This overwrote the value of facet.field with the last seen/parsed value i.e. there was only one value in the end. This is expected as that's noggit's behavior i.e. doesn't complain and just overwrites the previous value with the same key.