Export fails when exporting a Test Step Custom field from Iterations of a custom Test Type (Steps Kind)

Description
The export fails when you try to export a Test Step Custom field from an Iteration of a Test Execution when it´s a custom Test Type of the Steps Kind.

How to reproduce

1. Create a Test Step Custom field (Text Type)
2. Create a custom Test type of Steps Kind
3. Create a Test issue and select the custom Test Type
4. Add a simple Dataset to the Test so it generates Iterations
5. Execute the Test
6. Go to the Test Execution and try to export the Test Step custom field from the Iterations

Actual result/Attachments
The export will crash.

Expected result
It should not crash and export the field.