create validator to check if the issue links "duplicates" or "duplicated by" exist on transition

[Natalia Trofimov]

I would like to create a validator to check if the issue links "duplicates" or "duplicated by" exist on the transition to "Duplicate" and then add the pop-up screen with the linked issue field and make it mandatory if the "duplicated" issues don't exist. 

I created the validator for "duplicated by" link and it works but I want to show the linked issue screen only if "duplicated" (duplicated by or duplicates) links don't exist on the transition to "Duplicate"