This is the documentation of JSU for Jira Cloud. If you are using JSU on Jira Server or on Jira Data Center, you can find the documentation here.
In JSU for Jira Cloud there is no "Clear Field Value" post-function. But It can be achieved using "Copy Value From Other Field" post function. It clears the value of a specified field, after a transition has been completed.
You must specify the source field as "***empty***" and destination field which needs to be cleared. For example:
For information on how to configure a post-function in Jira, see the Jira documentation.
A workflow is configured so that the 'Close' transition has the '"Copy Value From Other Field" post-function to clear any field. The function is configured to clear the 'Security Level' field. If a user closes an issue on this workflow, the value of the 'Security Level' field will be cleared.