Tried the following JSON input as a simple test of generating terms using a script in the visualize aggregation builder:

{ "script" : "doc['gender'].value" }

but got a fatal error (GroovyScriptExecutionException[ArrayIndexOutOfBoundsException[null]. I think this is because Kibana is still sending the term field, which should be omitted with this kind of script.

I did get a value script to work:

{ "script" : "'Test: '+_value" }