Testing:

- In a project:

- insert a symbol of any standard component

- Assign a part number

- try to set its quantity value to 0.  (It should work.)

- Try to set its quantity value to -1, you should get an error.

- Insert a couple of more of the same previously inserted symbol, and assign the same part number.

- Show the BOM view and verify that teh quantity adds up (taking into consideration the '0' in one of the component's quantity value...)