Mandatory custom fields on resolve only

Hi list,

I’d like to know if it is possible to create a custom field that would be
mandatory on resolve only. Meaning that I can create a ticket and leave it
set to (no value).

If someone could show me some code or give me pointers as to how to do it,
it would be appreciated.

I am using RT 3.6.4.

Thank you very much,

J-P