BitLocker recovery key not returned even though selected

[richardpauly]

Describe the bug
When querying BitLocker Recovery keys through the Microsoft Graph API, version 1.0 no key is returned even though it is part of the select query header, except when key is the only selected property.

I do realize that this is not specific for the Graph Explorer, but I don't know where else to report this.

To Reproduce
Steps to reproduce the behavior:

1. Ensure the client has the BitlockerKey.Read.All permission
2. Query https://graph.microsoft.com/v1.0/informationProtection/bitlocker/recoveryKeys/{recoveryKeyId}/?$select=key - all properties, including the key is returned
3. Query https://graph.microsoft.com/v1.0/informationProtection/bitlocker/recoveryKeys/{recoveryKeyId}/?$select=key,id,createdDateTime,deviceId - the properties id, createdDateTime and deviceId is returned but not the key.

Expected behavior
All selected properties, including key, should be returned when using the statement $select=key,id,createdDateTime,deviceId.