How to use variable name inside alert.email property ?

i have a the following script :
`|eval(lambda: regexReplace(/\.\S+\.[0-9]+/,"project",'@gmail.com'))
.as('userid')
.keep()
|alert()
.id('kapacitor/{{ .TaskName }}')
.email(userid)`

This gives me the error :
invalid TICKscript: name "userid" is undefined. Names in scope: time,batch

Start with the TICKscript using eval(), alert(), and email(userid), then inspect how alert email properties and variable scope are validated. Reproduce the reported undefined-name error and determine whether variable-based email values are supported; document the supported behavior or define the required change.

Written by the indexing model from the issue text.