Get external task topic name via expression

Hi Guys.

I have a simple process with two external tasks:
Imgur

These are the task properties:
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task.1 has the topic name TASK.1
task.2 has the topic name TASK.2

Also, these tasks have Start Listeners:

This is the expression:

${execution.getProcessEngineServices().getRuntimeService().
createMessageCorrelation("CAMUNDANEWTASK").
setVariable("CurrentActivityId",execution.getCurrentActivityId()).
setVariable("ProcessDefinitionId",execution.getProcessDefinitionId())
.setVariable("ProcessBusinessKey",execution.getProcessBusinessKey()).
setVariable("ActivityInstanceId",execution.getActivityInstanceId()).
correlateWithResult()}

I wanna add to this expression the topic of current activity. How can I do this?