Content entries with a null creationdate fails import to Cloud

Issue Summary

Currently, Confluence Server allows content to have a null creationDate which is something not supported in Confluence Cloud.
These conditions will make an import from server to Cloud fail.

Steps to Reproduce

1. Export a Space from Confluence Server.
2. Import the Space to Confluence Cloud.

Expected Results

Space is imported successfully.

Actual Results

Space import fails and the following error is thrown in the UI:

com.atlassian.confluence.importexport.ImportExportException: org.springframework.transaction.UnexpectedRollbackException: Transaction rolled back because it has been marked as rollback-only

Workaround

Find the affected content entries and update them through the database.
To find the entries:

select contentid,contenttype,content_status from content where creationdate is null

Suggestion

Add a constraint to the content table so the creationdate column can not be null.