Jira Workflow Toolbox: adding labels to existing values in the label field

[Katharina Flor]

Hi,

i am using Jira Workflow Toolbox and i want to add a Workflow post-function that adds during a specific transition, a label to the issue - add this label to already existing values in the label field.

How can I write the parser expression for it? With the current configuration, existing labels will be replaced.