Upgrade from D6 to D7 failed because of absent field in the DB

I am trying to upgrade my D6 installation (with Node Gallery) to the D7. In the process of DB update for modules I have got an error:

node_gallery module
Update #7001

Failed: FieldException: Attempt to update an instance of a nonexistent field . in field_update_instance() (line 525 of /data/redrat/soft/drupal7/core/modules/field/field.crud.inc).

After some code digging I have find out that problem is in the node_gallery_create_thumbnail_node_view_mode() call, which in turn call field_info_instance(). But field_node_gallery_image doesn't exist yet at time of DB update, because this field had to be migrated from D6 to D7 by 'content_migrate' module of CCK.

Thus to upgrade D6 Node Gallery to D7 you need at first install a CCK Content Migrate module, migrate image field for galleries, and only after that install and update Node Galley module. So, I think this had to be documented somethere.