Parallels Cloud Server 6 virtual machine templates stored on an SMB share cannot be modified via PVA MN interface.
The following error occurs:
Operation is finished with errors: Can not set: RDBMS error (102) : DB Error 1048 (Column 'objId' cannot be null) in query INSERT INTO `ObjectsTreeLink` (`objId`) VALUES (NULL)
The problem is recognized as a product bug with internal ID PVA-33885.
The fix will be included in one of the future updates of Parallels Virtual Automation.
The error is not harmful - the changes are still applied, so it can be safely ignored.