Repro steps:

1) Create UML Java-Platform project
2) Create class diagram with two classes named Customer and Product
3) Select Association Class in the diagram palette, and draw link from Customer
to Product: the new association class is created - name it Order

Generate source code and open the souces. No association relationship is shown
in the source for Customer and Prodcut relating to the association class.

Here are the generated sources:

public class Customer {
    public Customer() {
    }
}


public class Product {
    public Product() {
    }
}