How to make the fields Old Quantity/Old Value as required depending on the Opportunity Type field

Question :

**This post was created as part of a How to Service Request (SR)

Release: 

22B

Summary of the question:

How to make the fields Old Quantity/Old Value as required depending on the Opportunity Type field ?

For the object Opportunity Revenue I've added two custom fields Old Quantity and Old Value . I want to set the fields as required depending on the value in the Opportunity Type filed. When the value in the Opportunity Type is Renewal, the fields Old Quantity and Old Value must be required and marked with a star (*), else not.

I used the next groovy script :