Meaning of first empty column in CSV API result

I’m always getting an empty field for all CSV rows I get from an API flux query. Where it is documented ? How can I use it ?

Here is my sample results

,result,table,_time,_value,_field,region
,hello,0,2021-06-14T11:31:43.512Z,0.72,value,us-west
,hello,0,2021-06-14T11:31:47.257Z,0.72,value,us-west

,result,table,_time,_value,_field,region
,hello,1,2021-06-14T11:31:43.512Z,42,value2,us-west
,hello,1,2021-06-14T11:31:47.257Z,42,value2,us-west

Please can you show us the query you are using?

Antony.

    from(bucket: "test")
        |> range(start: -20m, stop: now ())
        |> filter(fn: (r) => r["_measurement"] == "cpu_load_short")
        |> filter(fn: (r) => r["host"] == "server01")
        |> keep (columns: ["_time", "_field", "_value", "region"])
        |> yield (name: "hello")