Validates that specified field (can be a custom field) has been set
To add Field has been set validator, go to the transition of your workflow, switch to Validators tab and click on Add Validator button.
Select JEP - Field has been set validator and click Add button
Select the field which you want to be set to allow the transition.
That's it, the validator is added to the transition.
If the field has not been set but the user tried to perform the transition, below error message is displayed.
Do not forget to publish the workflow.