GUI failed to create a monitor in a monitored server detail page

When the users are on the server details page,
Steps to reproduce:

1. Go to a server detail page which is monitored by some monitor
2. Click `+ Create New" button and choose to create a new `Monitor`
3. Fill in all required inputs
4. Ignore the `Servers` relationship dropdown
5. Click `Save`

Expect:
A new monitor is created

Actual:
Failed to create the monitor and the snackbar message shows
"Server 'server_name' is already monitored by 'monitor_name', cannot add it to another monitor.
Could not create monitor 'new_monitor' with module 'mariadbmon'"