Example Query Expression, URL and Results:
http://DA:8581/odata/api/groups?$expand=devices,components&$select=Name,devices/ID,devices/HostName,components/ID,components/Name,components/DeviceItemID&$filter=((Name eq 'top group'))
The group contains no devices.
Release : 20.2
Component : DX Netops Performance Management
As the group does not contain devices, the device ID and hostname fields in the results would not be populated.