As an HP Importer I can import Tests with Link Test set to zero

As an HP Importer I can import Tests with Link Test set to zero.

In HP ALM/QC:

1. When a Test calls a Template Test the Link Test is set with the ID of the Template Test.
2. When the Test case does not call any Template Test the Link Test is NULL.
3. However, when a Template Test is deleted, all the Test that were calling it get a 0 (zero) in the Link Test, when it should get a NULL value.

Because Xray only imports Tests without calls, it would be good to be able to import also the Tests which have the Link Test as 0 (zero).