Affected Version: 2.11+
What steps will reproduce the problem?
1. Create a "Registered Users" group with the SSH command: ssh -p 29418 localhost gerrit create-group '"Registered Users"'. Gerrit doesn't prevent this and the group is created.
2. Now if you attempt to configure access rules with "Registered Users" group it will use this newly created group instead of the system group.
What is the expected output? What do you see instead?
Users should not be able to create internal groups with the same names as systems groups.
Please provide any additional information below.
This works as expected from the Gerrit UI  and from the REST API. It also works as expected if you attempt to create duplicate internal group.
 With an Admin account, attempt to create a "Registered Users" group from the Gerrit UI. Gerrit won't allow it, the response is "Resource already exists".
 curl -X PUT --digest --digest --user $user:$pasword http://localhost:8080/a/groups/Registered%20Users
Response is "Group already exists"