Ginq: combining join and aggregate functions

Hi, I am trying to learn Ginq and are having problems with joining an 
aggregation functions.

The following example illustrates the issue:

import java.time.LocalDate

class Warehouse {
     int id
     String name
     Double price
     int stock

     Warehouse(int id, String name, Double price, int stock) {
       this.id = id
       this.name = name
       this.price = price
       this.stock = stock
     }
   }

   class Sales {
     LocalDate date
     int item

     Sales(LocalDate date, int item) {
       this.date = date
       this.item = item
     }
   }


List<Warehouse> warehouse = [
     new Warehouse(1, 'Orange', 11, 2),
     new Warehouse(2, 'Apple', 6, 3),
     new Warehouse(3, 'Banana', 4, 1),
     new Warehouse(4, 'Mango', 29, 10)
]
List<Sales> sales = [
     new Sales(LocalDate.of(2024, 5, 1), 1),
     new Sales(LocalDate.of(2024, 5, 2), 1),
     new Sales(LocalDate.of(2024, 5, 3), 3)
]
def q = GQ {
   from s in sales
   join w in warehouse on w.id == s.item
   select w.name, w.price
}
// so far so good, the following works:
assert  [['Orange', 11.0], ['Orange', 11.0], ['Banana', 4.0]] == q.toList()

// now try to summarize by name
def qSum = GQ {
   from s in sales
   join w in warehouse on w.id == s.item
   groupby w.name
   select w.name, sum(w.price)
}
// Fails with Exception evaluating property 'price' for groovy.lang.Tuple2,
// Reason: groovy.lang.MissingPropertyException: No such property: price 
for class: Sales
assert  [['Orange', 22.0], ['Banana', 4.0]] == qSum.toList()

So for some reason ginq thinks it will find the price property in the 
Sales class instead of in the Warehouse class so w.price here is not 
understood. What is the right way to write it?

Regards,

Per