SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'nid' cannot be null

I recently updated the Flag module to 7.x-3.9 from 7.x-2.0 which went through fine.

When I then tried to import a CSV file that is meant to create new nodes under a content type, I get the below error:

SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'nid' cannot be null

I rolled back the changes to the Flag module and used a previous DB to test, and the upload works fine with that. The issue appears to be when the Flag module is updated.

Understandably, if this is meant to be in the Flag issue queue let me know and I'll raise the issue there.