Use the 'Fields Required' workflow validator that is packaged in the JIRA Suite Utilities.
Please note the following caveats regarding validation of data by the 'Fields Required' workflow validator at the time of issue creation:
- fields that you set up as "required fields" are not flagged as such in the form to the end-user
- such fields can be cleared at a later time, which is not what you may have intended
- plugins such as GreenHopper will not detect the requirement as implemented by the workflow validator, so may fail later during usage