Steps to reproduce
Start a Jira 7.13.x instance and create a synchronization
Configure workflows to be synchronized
Do not add a resolution field mapping
Do not add the resolution field to the transition screen of the second side's workflow
Start the sync
Synchronize an issue and move it to a status with a resolution
The issue is synchronized without problems.
Jira throws an error because Backbone also tries to set the resolution when transitioning the issue.