Importing issues from CSV with Epic link, Parent and Subtask shows the validation successful but import fails to import the subtask

Issue Summary

Importing issues from CSV with Epic link, Parent and Subtask shows the validation successful but import fails to import the subtask. After the import fails, if you go back in the browser the validation page shows the validation error as in the screenshot attached.

Steps to Reproduce

Case 1

• Create a project ABC, create an EPIC ABC-1.
• Now, try to import a task and a subtask which are the issues in the epic. A sample CSV is attached.
• Import the CSV, Map the EPIC link, Parent ID, Issue ID, Description, Summary, Issue type
• Validation > Success
• Import > Fails to import the subtask

Case 2

• Import the CSV, Map the Parent ID, Issue ID, Description, Summary, Issue type
• Validation > Success
• Import > Success, both the Parent and Child tasks are imported but not mapped to the EPIC.

The Case 1 test is working perfectly fine if you try from External system import.

Expected Results

Jira should atleast throw a warning stating that the import would fail in the Validation step.

Actual Results

The below exception is thrown in Case 1, import log.

2020-12-04 16:42:56,380 ERROR - Fatal error during import
java.lang.IllegalArgumentException: Sub-Task Issue cannot be null.

Workaround

The Case 1 test is working perfectly fine if you try from External system import.

Note

In some cases, {}changing the CSV order by defining the epic and stories then the subtasks below them seems to help in Case 1.