d6_node_revision sometimes doesn't have anything to migrate, then fails checkRequirements?

I stumbled upon this issue while testing a very simple D6->D8 node migration (https://drupal.org/node/2233883), and thanks to benjy, I was able to track it down enough to the point where we think it is an actual issue.

tl;dr;

The d6_cck_field_revision migration has a hard dependency on the d6_node_revision migration, but when there are no non-active (?) revisions in the source DB, the d6_node_migration doesn't have anything to migrate, so it fails checkRequirements().

Background

I started with a new D6 site, enabled CCK's "Content" and "Link" modules, then added a simple link field to the "story" content type. I added one "story" node and one "page" node.

I also created a fresh D8 site, enabled the migrate_drupal and link modules.

Initial test

I ran a node migration using the manifest from https://drupal.org/comment/8652693#comment-8652693.

~/Sites/imp $  drush migrate-manifest mysql://imp@localhost/drupal6 manifest.yml
Migration d6_cck_field_revision:page did not meet the requirements                                                                                                              [error]
Migration d6_cck_field_revision:story did not meet the requirements 

I then stepped through the code and found that the d6_node_revision migration wasn't passing checkRequirements and returning FALSE on

// If the dependent migration has not processed any record, it means the
        // dependency requirements are not met.
        if (!$required_migration->getIdMap()->processedCount()) {
          return FALSE;
        }

I checked my D8 database and saw that there were 2 node_revision records (one for each of my 2 nodes), but no records in the migrate_map_d6_node_revision table.

Theory

Clearly, revisions were being created, but not by the d6_node_revision migration. I'm thinking that the two revisions I see are the result of the d6_node migration, as these are the current revisions for my 2 nodes. This would explain why we have 2 revisions, but nothing in the migrate_map_d6_node_revision table.

Because the d6_cck_field_revision has a hard dependency on d6_node_revision, when it checksRequirements and fails, d6_cck_field_revision never runs.

Solution?

Perhaps the way to solve this is to have the d6_node migration add an id mapping for the revision it creates?

-mike