Subquery Equality Filtering on Computed Column Failing

[robertervin]

Plywood.ply()
      .apply("my_datasource", $("my_datasource")
          .filter(
            $("timestamp").in({
              start: new Date("2018-01-01"),
              end: new Date("2018-02-16")
            })
      ))
      .apply('visitorTypes', $("my_datasource")
             .split({ UserId: '$user__id' })
             .apply('user__is_new', $("my_datasource").max('$user__is_first_session')))
      .apply('data', $("my_datasource")
             .filter($('user__id').in(
                $('visitorTypes').filter('$user__is_new == 0').collect($('UserId'))
              ))
             .count())

Created a POST request of

{  
   "method":"POST",
   "url":"https://example.com/druid/v2/",
   "body":{  
      "queryType":"timeseries",
      "dataSource":"my_datasource",
      "intervals":"2018-01-01T00Z/2018-02-18T19:35:30.768Z",
      "granularity":"all",
      "context":{  
         "timeout":10000
      },
      "filter":{  
         "type":"or",
         "fields":[  

         ]
      },
      "aggregations":[  
         {  
            "name":"__VALUE__",
            "type":"count"
         }
      ]
   },
   "headers":{  
      "Content-type":"application/json"
   }
}

Which makes Druid throw

Error: Unknown exception: Instantiation of [simple type, class io.druid.query.filter.OrDimFilter] value failed: OR operator requires at least one field (through reference chain: io.druid.query.filter.OrDimFilter["fields"])

Since the dataset $user__is_new is a member of is in-memory, Plywood should filter in-memory instead of passing through to Druid.

Also of note, if I use a quantile filter instead of an equality filter (e.g.

 .filter($('ad__id').in(
    $('adsByCTR').filter('$ad__ctr <= $adsByCTR.quantile($ad__ctr, 0.25)').collect($('AdId'))
))

it works as expected.