upgrade from 2.x to 3.x Synchronizing step hangs when a group repo is empty because its members already exist in Nexus 3

1. delete all repos in Nexus 2 ( for a clean test )
2. create a Maven 2 proxy repo in nexus 2 named maven-central
3. create a Maven 2 group repo in Nexus 2 with maven-central as the only member.
4. attempt to upgrade nexus 2 to nexus 3.x
5. The repository selection screen in the migration wizard selects the group repo and does not select the maven-central repo because Nexus 3.x already ships with a repo named maven-central.
6. Proceed with the migration. Problem: On the Synchronizing step of the migration wizard the Continue button will never become enabled - preventing migration from completing.

Expected

• The empty group repo will not created in Nexus 3
• the continue button will become enabled on the synchronizing step allowing a user to complete the migration 

Workaround

You have 2 options to complete the migration. Either:

1. Choose not to migrate the group repository that will have an empty members list
2. Before starting migration to Nexus 3, delete the existing maven-central repository from Nexus 3. Sign in as admin, select the repository in the repository list and delete it. Then when you start migration, the nexus 2 maven-central repo will be selected to migrate and the group repo will not be empty, so it will migrate as well.