Unable to print the value for a condition

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Hi All,

Wrote the below tick scripts to print the field "Duration" in the slack channel for the condition of "target". However, the below seems to be not giving any alerts in the slack channel

```
var period = 2s
var every = 2s
var data = stream

|from()
.database('asgbackup')
.retentionPolicy('autogen')
.measurement('drive_info')
.where(lambda: "target" =~ 'Mysqltest6')
.groupBy(*)
|window()
.period(period)
.every(every)
|alert()
.message('Duration: {{ index .Fields "duration" }}')
.crit(lambda: TRUE)
.slack()
.log('/var/tmp/kapacitor/files.log')
```

Could you please help in what might be wrong..

The provided TICK script is the only entry point mentioned; start by reproducing it with the stated database, measurement, condition, and Slack output. Inspect the alert log and message rendering to determine why no alert is emitted, and consider the issue done when the condition produces a Slack alert containing the Duration value.

Written by the indexing model from the issue text.