How to change value from null to empty collection for a list attribute when saved from Backoffice ?

Hi Experts,

I'm using version 6.4. When saving a particular item from backoffice, which has an attribute of type 'Collection', it is getting saved as null. But when saved from HMC, it is getting saved as an empty collection. I want the same behavior from backoffice too. How can this be obtained ? Should I change the editor ? Or use a custom editor ? Please help.

Thanks in Advance.