Fullname function not working when exporting User Picker fields

Description
When exporting User Picker fields with the Fullname function, the field is not exported.
Formatting User Picker Fields

How to reproduce

1. Create a template to export a User Picker field ( for example: Reporter or Assignee)
2. Add to the mapping the fullname function
   
3. Export it in a Issues with those fields filled in.
   

Actual result/Attachments
The field with the fullname function doesn´t export anything.

Expected result
It should export the fullname of the User.