Make the default for the HandleTemplate to use Handle::default().

[andriyDev]

Objective

• Not setting any value to a handle in BSN results in BSN attempting to load an empty path! This is not handled well (see Return/log an error when attempting to load an empty asset path. #23654 for some fixes there).
• Even with Return/log an error when attempting to load an empty asset path. #23654, we would still get errors in the logs which is not ideal.

Solution

• Use the Handle variant for the template!