Can't calculate SUM with FLUX

[KlausH1967]

Hello,
I try to create a diagram to compare to timeframes by using timeShift in FLUX-Syntax.

When I'm using InfluxQL I get the data in correkt form.
Syntax:
SELECT sum("value") AS "sum_value" FROM "statistik"."autogen"."kWh" WHERE time > :dashboardTime: AND time < :upperDashboardTime: AND "deviceName"='solaranlage_erzeugung' AND "duration"='h' GROUP BY time(2h) FILL(null)

By usind FLUX I get the message: "panic: runtime error: invalid memory address or nil pointer dereference"
Syntax:
from(bucket: "statistik/autogen")
|> range(start: v.timeRangeStart, stop: v.timeRangeStop)
|> filter(fn: (r) => r["_measurement"] == "kWh")
|> filter(fn: (r) => r["deviceName"] == "solaranlage_erzeugung")
|> filter(fn: (r) => r["duration"] == "h")
|> filter(fn: (r) => r["_field"] == "value")
|> group(columns: ["field"], mode:"by")
|> aggregateWindow(every: 2h, fn: sum)

The same query works fine to calcualte the max-value:
from(bucket: "statistik/autogen")
|> range(start: v.timeRangeStart, stop: v.timeRangeStop)
|> filter(fn: (r) => r["_measurement"] == "kWh")
|> filter(fn: (r) => r["deviceName"] == "solaranlage_erzeugung")
|> filter(fn: (r) => r["duration"] == "h")
|> filter(fn: (r) => r["_field"] == "value")
|> group(columns: ["field"], mode:"by")
|> aggregateWindow(every: 2h, fn: max)

Systeminformation:
Version | core-2025.2.4
Installationstyp | Home Assistant OS
Entwicklung | false
Supervisor | true
Docker | true
Benutzer | root
Virtuelle Umgebung | false
Python-Version | 3.13.1
Betriebssystem-Familie | Linux
Betriebssystem-Version | 6.6.62-haos-raspi
CPU-Architektur | aarch64
Zeitzone | Europe/Vienna
Konfigurationsverzeichnis | /config

Addon:
InfluxDB (5.0.2),
Grafana (10.4.2),

At the logfile I found following line:
time="2025-02-24T21:44:34+01:00" level=info msg="Response: Internal Server Error" component=server method=POST remote_addr="127.0.0.1:44268" response_time=687.99701ms status=500