Has Assignee Validator
With this workflow post-function, you can ensure that issue has or not an assignee before to execute this transicion.
To add 'Has Assignee Validator' to a transition:
Click Edit for the workflow that has the transition you wish to add the validator on.
In the Workflow Designer, select the transition.
Click on Validator in the properties panel.
Click on
Add
validator
.Select
Has Assignee Validator
from the list of validators.Click on
Add
to add the validator on the transition.Fill the form shown below and press 'Add' button.
Fields
Default Message – Set here the message you want to display o users when this validation fails