I have created a very simple test load file for bulk loading Tasks and sub-tasks as per the Import data from a CSV instructions.
Issue ID, Parent ID, Issue Type
I have mapped the Issue ID to Issue ID in the import config
and Parent ID to Parent ID in the import config
When I load I get a fatal error advising that Parent can't be NULL, but it is not NULL.
I have previously validated all of the other values to be loaded with no errors so it is not a rogue validation error.
How can I resolve this problem please?
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Your file looks technically correct to me, but I have a nagging doubt that it doesn't like the empty issue id on the sub-task line.
When I do imports with sub-tasks, I've always done it with the issue id populated for all issues, even though I really don't need it on the sub-tasks. So my files would look like
So two issues, one with two sub-tasks.
I once had a problem with the order as well - for some reason, I'd put a sub-task above the issue it was part of, and that failed to import, presumably because Jira was reading one line at a time, but that was in a very old version of Jira and I don't think it goes line by line any more, I think it reads the whole file and works out which issues need creating before their sub-tasks.
That suggests you have a line that names a sub-task issue type, but has no parent ID filled.
One thing to try is filling in every line with a parent id - for the issue level issues, use their own id as the parent (jira should ignore the field for issue level issues)
Re-using my example with that tweak, you would import: