Hello, I have 4 custom fields: "customer priority", "Impact", "Urgency" and "calculated priority".
When customer priority is empty, Impact = "high" and Urgency 'High" then calculated priority = 1.
I need to calculate this at Create Issue, so user fills in value for Impact and Urgency and leaves Customer Priority empty and Jira calculated the Calculated Priority.
I understand I can't do this in a Post function, because the values are not stored in database yet, from this article (https://community.atlassian.com/t5/Jira-questions/Making-a-JIRA-field-required-based-on-a-value-chosen-on-the/qaq-p/247284) I understand I have to user Validator to retrieve chosen value of Customer Priority, Urgency and Impact to calculate my Calculated Priority. But which Validator do I use and how? 
