Spawner Admin page shows all the users from groups but cannot spawn for who never logged in

Description of problem:

Administration page in Notebooks Spawner has records for every user from the groups which are set as RHODS admins and basic users. But, if an admin tries to spawn a notebook server for a user who never logged in the dashboard, the process fails to start with the following error message:

Request invalid against a username that does not exist.

I see this affecting user experience for the administrators

Prerequisites (if any, like setup, operators/versions):

Steps to Reproduce

1. Log in RHODS as admin
2. Launch Jupyter from Enabled page
3. move to Administration tab
4. choose a user who never logged into dashboard from the table
5. click "start server"

Actual results:

spawning process fails

Expected results:

TBD

Reproducibility (Always/Intermittent/Only Once):

Always

Build Details:

RHODS v1.21.0-20 (but valid for previous versions too)

Workaround:

make the target user logging in Dashboard once

Additional info:

Some possible options I see are:

1. avoid to show the "start server" action for the users who haven't logged in yet
2. do not show users who haven't logged in yet
3. change the error message to something more clear
4. make the start process possibe even if a user haven't logged in yet