Email Notification sends errors after issue move with new priority.

Summary

Email notification when an issue is moved from Software to Service Desk project that has newly associated priority scheme and priorities.

Steps to reproduce:

You need outgoing mail activated.

1. Create a new priority scheme with new priorities.
2. Associate new priority scheme with a Service Desk Project.
3. Create an issue in a Jira Software project.
4. Move the issue from the Software to the Service Desk Project.
5. Select one of the priorities(from the new scheme) as the new priority in the issue.

Expected Result:

The Issue is moved to the new project and a notification is sent informing the participants that the issue was moved.

Actual Result:

The issue is moved to the new project correctly but the e-mail sent has the following error message:

An error occurred whilst rendering this message. Please contact the administrators, and inform them of this bug. Details: ------- org.apache.velocity.exception.MethodInvocationException: Invocation of method 'getPrettyFieldString' in class com.atlassian.jira.util.JiraVelocityHelper threw exception com.atlassian.jira.issue.customfields.impl.FieldValidationException: Invalid priority name 'Medium (not available)'. at templates/email/html/includes/fields/changelog.vm[line 32, column 50] at org.apache.velocity.runtime.parser.node.ASTMethod.handleInvocationException(ASTMethod.java:337) at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:284) at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:262) at org.apache.velocity.runtime.

Workaround:

There's no workaround to prevent this from happening. The error message is only sent when the issue is moved, the subsequent notifications(comments, status changes) are sent correctly with no errors.