Validate that the Checklist is Not Empty
This validator blocks a transition unless there are checklist items, either on a Local or Global Checklist.
Company-managed Projects
To set the workflow validator:
Navigate to Project Settings > Workflows
Click the pencil icon to edit the workflow.
Select Diagram mode and click on the transition where you want to add the validator.
Click on Validators.
Click Add validator.
Select the Checklist is not empty validator and click Add.
Click Add again to confirm creation of the validator.
Click Publish draft to save the changes.
Test the validator by attempting to transition an issue which does not meet the criteria. The transition will fail.
Troubleshooting Validators
Checklists for Jira uses work item entity properties to provide the following features:
Therefore, the Checklist must be able to set work item entity properties. This is enabled by default. However, if a jira.permission.* workflow property has been set on a workflow step, Checklists may not be able to set issue entity property.
For example, the following property will prevent Checklists from setting work item properties, and features listed above won't work correctly:

Removing the jira.permission.* workflow property and using the standard Jira permissions to control who can edit the work item will allow the Checklist functions to work.
Team-managed Projects
You can create a rule in a Team-managed project that will block a transition unless there are items in the checklist.
To create the rule:
Navigate to Project settings > Work types.
Select the appropriate work type. Use the Search all fields box to find the Checklist Completed custom field and drag it to the appropriate place on the layout. Click Save changes.
Click on the Edit workflow button.
Click Rule.
Select Validate details as the Rule type, and choose Validate a field. Click Select.
Select the appropriate transition.
Use the Validate that field dropdown to select Isn’t empty.
Select Checklist Text from the For fields(s) list.
Click Add.
Click the Update workflow button to publish the rule.