Conversion to Scroll Documents fails when deleting included page

Steps to reproduce

1. Create a space with a version

2. Include Page A through a include+ macro on Page B

3. Completely delete Page A (from all versions)

4. Migrate the space to Scroll Documnets

Expected behavior

The space migrates and Page B has a broken include macro.

Actual behavior

The migration fails with a NullpointerException.