There are several different ways of blocking the issue workflow transition:
- Block transition if any item from the checklist is not completed (built-in validator).
- Block transition if the checklist is empty (build-in validator).
- Block transition using regular expression (custom validator; allows to make particular items optional or check if there are any items).
In Jira, the transition between workflow statuses goes through a validation phase that determines if the transition is allowed or not. The validation phase can be configured by Jira administrators through "validators". Learn more about Configuring Workflows and Workflow Validators in the Atlassian Documentation.