My JPQL query with Outer Join returns empty list while using GroupBy, OrderBy and Sum Function - jpa

Question

This is my Product entity:
#Entity
public class Product {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#NotBlank
private String name;
#ManyToOne(cascade = { CascadeType.PERSIST, CascadeType.MERGE })
private Category category;
...
}
And this is the productOrder junction table for the relation product-order:
#Entity
public class ProductOrder {
#EmbeddedId
private ProductOrderId pk;
#Min(value = 1)
private int quantity;
...
}
And this is the embeddedId class:
#Embeddable
public class ProductOrderId {
#ManyToOne
#JoinColumn(name = "product_id")
private Product product;
#ManyToOne
#JoinColumn(name = "orderr_id")
private Order order;
...
}
I have this JPQL Query works perfectly which finds all the products from a category, sorting them based on their total sold quantity. Since it is a outer join, i get also the ones which haven't been sold yet:
#Query(value = "select p, sum(po.quantity) as total_quantity " +
"from ProductOrder po " +
"right join po.pk.product p where p.category = (?1) " +
"group by p.id, p.name " +
"order by total_quantity desc nulls last")
Page<Object[]> findBestSellerProductsByCategory(Category category, Pageable pageable);
The problem is, when there is not any sold product in a category, i get an empty page. So in order to use this query, my category has to have at least 1 sold product, then i get also the others which haven't been sold yet. What is the problem here?
Since i make a "select from junctionTable (ProductOrder)", when there is not any element from the category in this table, i get an empty list as i understand. But i could not make it the other way around "select from product", since product has no reference of productOrder table, i cannot make a join relationship in that case..
INFO: When i remove the groupBy, it works. I get my products from a category even if none of them is sold yet.
#Query(value = "select p " +
"from ProductOrder po " +
"right join po.pk.product p where p.category = (?1)")
Page<Object[]> findProductsByCategory(Category category, Pageable pageable);