Deadman {{ index .Tags "source_id" }} not working

I'm trying to use Chronograf, version 1.8.4, to generate a TICKscript to be used in Kapacitor, version 1.5.5. I'm not able to access Tags or Fields from the deadman. I want to see when data is not put into a measurement ('location') for a minute and get the `source_id` that triggered the deadman to go off. When I receive the email, I get: `Tags: map[] Fields: map[emitted:0]` in the subject line. If I do `{{ index .Tags "source_id" }}`, I get `Tags: Fields: map[emitted:0]`.

I saw an issue here: #2180 but it doesn't seem to have been resolved really.

```
var db = 'msatestbed'

var rp = 'autogen'

var measurement = 'location'

var groupBy = ['source_id']

var whereFilter = lambda: ("source_id" == 'id0')

var period = 1m

0s

var name = 'Test-location'

var idVar = name + '-{{.Group}}'

var message = 'Tags: {{.Tags}} Fields: {{.Fields}}'

var idTag = 'alertID'

var levelTag = 'level'

var messageField = 'message'

var durationField = 'duration'

var outputDB = 'chronograf'

var outputRP = 'autogen'

var outputMeasurement = 'alerts'

var triggerType = 'deadman'

var details = 'Test'

var threshold = 0.0

var data = stream
|from()
.database(db)
.retentionPolicy(rp)
.measurement(measurement)
.groupBy(groupBy)
.where(whereFilter)

var trigger = data
|deadman(threshold, period)
.message(message)
.id(idVar)
.idTag(idTag)
.levelTag(levelTag)
.messageField(messageField)
.durationField(durationField)
.details(details)
.stateChangesOnly()
.email()
.to('email@server.com')

trigger
|eval(lambda: "emitted")
.as('value')
.keep('value', messageField, durationField)
|eval(lambda: float("value"))
.as('value')
.keep()
|influxDBOut()
.create()
.database(outputDB)
.retentionPolicy(outputRP)
.measurement(outputMeasurement)
.tag('alertName', name)
.tag('triggerType', triggerType)

trigger
|httpOut('output')
```

Start by reproducing the Chronograf 1.8.4-generated TICKscript with Kapacitor 1.5.5, focusing on the deadman node's alert message and the reported empty Tags map. Trace how deadman alerts populate tags and fields, then verify that source_id is available in the email output while preserving the existing emitted field behavior.

Written by the indexing model from the issue text.