fill() seems to have no effect

(Also posted to https://community.influxdata.com/t/kapacitor-fill-seems-to-have-no-effect-on-batch-queries/2825)

I’m trying to compute summary data over series data that may have gaps. I would like to fill with the previous value in case of gaps. My tickscript looks like this:

```
var SQL = '''SELECT "duration"
FROM "desktop_client"."default"."profiling_metrics"''''

var hour_batched = batch
|query(SQL)
.period(1h)
.every(1h)
.groupBy(*)
.align()
.fill('previous')

var hour_median = hour_batched
|median('duration')
.as('hour_median')
|influxDBOut()
.database('desktop_client')
.measurement('kapacitor_experimental')
```

Any value I use for .fill() (previous, 0, null, etc.) yields the same results, and hours with missing values in the original series are also missing data in the transformed series. I have tried putting ‘GROUP BY/FILL’ in the influx query as well, with no results.