Issue Summary

Feature Import: Modifying a feature via the export template importing an empty cell for Parent Epic causes the UI to NULL the previous value.

Steps to Reproduce

1. Step 1 - Export a feature with a Parent Epic associated
2. Step 2 - Null out the Parent Epic field via the export template
3. Step 3 - Re-import the data 

Expected Results

Per our help Article: https://help.jiraalign.com/hc/en-us/articles/115000088674\

The user shouldn't be able to overwrite data.

Article Snippet:

Update the import file
You can update items by importing them back to the system. If trying to update existing items, we do recommend exporting those items, and then copying that data into the import file.

The mapping is done based on an ID and/or name:

• If you enter an ID of an item, the item gets updated.
• If the item with the name already exists and the ID was not provided, this item is still updated.
• If you provide an invalid ID, the item will not upload.
• When you provide an ID from one item and an existing name from another, it will not be updated.
  * Blank cells do not override the values.

Actual Results

Parent Epic is overwritten when null values are in the export template (when re-importing)

Workaround

Navigate to the audit log find the previous value and make the necessary changes if the value was erroneously nulled out.