When you try to iterate over iterations that are not supported by other iterations Xporter throws an error

Short description: When you try to iterate over iterations that are not supported by other iterations Xporter throws an error

Steps to reproduce:

1. Install this template Software_Requirements_Traceability.xlsx in your instance
2. In a bulk export with issues with different issue types try to export the template installed in step 1 

Actual Result: Xporter throws an error

Expected Result: It should be possible to export.

To Do: It should be possible to export the template even if you are iterating over iterations that are not supported by other iterations.