Import- In Epics, Removing column "Release" removes the data from the updated epic

Issue Summary

The import function is used for a user to update an Epic via xml/xls file
During this process, a user can change the data needed via an Excel spreadsheet, and if a column is not updated, the user can usually remove this column, and the data would remain untouched for this field

The Release column, however, when removed, simply erases any data that is currently existing for the Release/ PI Field. 

This behaviour is not matching other columns that are working as expected (Remove column = untouched field in Jira Align) as well as not matching other work items, such as Features, where removing the release Column keeps the data in JA as expected

Steps to Reproduce

1. Export an epic or small list of epics from the epic page
   Make sure you select some with Release /PI filled in
2. Use the Import template and fill in the information from the export
3. Remove a few columns that you will not change, include Release as a column to remove
4. Perform a few changes in other columns, and Import the changes
5. Import the data to update the epic(s) you have made changes to
6. Notice that the updated columns are successfully updated
   Notice that the deleted columns keep original data, with the exception of the Release column

^{NOTE The Estimate column will also be affected as it is tied to a PI, once the PI is removed, the estimate is subsequently removed as a result}

Expected Results

The Column "Release" when not requiring an update and removed from the template by a user, should not remove the original data in the Epic,  as it is in other work items and other columns

Actual Results

The Release column, when removed, is deleting data as if it was set as empty, making the behaviour inconsistent with other columns and work items

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available