reference implementation of getPropertyDescriptor()

[Greene (US), Geoffrey N via users]

What is the  minimum or reference implementation of getPropertyDescriptor(name) 
in a groovy ScriptedLookup processor?

I don't have any properties, and I had been doing

@Override
     PropertyDescriptor getPropertyDescriptor(String name) {
        return null
     }

But I don't think that is correct.

Whats the correct/minimum implementation?  How do I create a property 
descriptor?