Fix duplicate key errors in PostDeployMigrateUserExternalMailData migration

`email_provider` by default is NULL, and if a user had not logged the
value would remain NULL. Upgrading to GitLab 10.0 would lead to a
PG::UniqueViolation because the post-deploy migration would attempt
to reinsert the entry because the NULL comparison between
`users.email_provider` and `user_synced_attributes_metadata.email_provider`
would never match.

Closes #38246

1 files changed, 1 insertions, 1 deletions

diff --git a/db/migrate/20170828135939_migrate_user_external_mail_data.rb b/db/migrate/20170828135939_migrate_user_external_mail_data.rb
index 592e141b7e6..395181a3b22 100644
--- a/db/migrate/20170828135939_migrate_user_external_mail_data.rb
+++ b/db/migrate/20170828135939_migrate_user_external_mail_data.rb
@@ -33,7 +33,7 @@ class MigrateUserExternalMailData < ActiveRecord::Migration
           SELECT true
           FROM user_synced_attributes_metadata
           WHERE user_id = users.id
-          AND provider = users.email_provider
+          AND provider = users.email_provider OR (provider IS NULL AND users.email_provider IS NULL)
         )
         AND id BETWEEN #{start_id} AND #{end_id}
       EOF