A K2 Workflow Instance goes into error state when an Email Escalation is executed with an error message:
"The parameter 'addresses' cannot be an empty string. Parameter name: addresses"
The issue will be encountered when a Workflow Task Recipient is set to a K2 Role and an Email Escalation is also configured to execute after a specified Time with "Send email to task participants" selected.
When the Email Escalation is triggered, the Workflow Instance will go into an error state.
The error is expected due to the way the Workflow is configured.
Because the Task is assigned to a K2 Role and it has not been opened yet, there is no individual users associated with the Task. When the Email Escalation is triggered, no users and therefore no email addresses are available to send the email to, causing the error.
Should Email Escalation be required on a Task assigned to a K2 Role, the "Resolve groups to individuals" option needs to be enabled on the Task Result Rule Tab under the Options section.
This will create a Task for the individual members of the K2 Role instead of the K2 Role directly. When an Email Escalation occurs, the mail will be sent to the specific user(s).