Previewing Snapshot of a vm, taken without hard disk throws Error Code: 500

Issue

• Issue is reproducible in following scenario:

Steps to Reproduce:
1. create a vm without hd attached
2. launch the vm
3. create a live snapshot
4. stop the vm
5. add a hd 
6. launch the vm
7. create a live snapshot
8. stop the vm
9. try to use first snapshot (which has no hd)

• Click on Preview snapshot. Following error message will popup in event tab:

Failed to preview Snapshot for VM <VM name> (User: admin@internal).

• But, snapshot(with no hd) will be in preview mode. Further try to commit the snapshot, following message appears on the screen:

Error: A Request to the Server failed with the following Status Code: 500

• Only Delete VM will work.