plsql深度嵌套集合初始化

create or replace type invoice_obt
as object (
invoice_id number
);
/

create type invoices_ntt
as table of invoice_obt;
/

create type customer_with_invoices
as object (
customer_id number,
invoices invoices_ntt
)

declare                                                        
l_customer customer_with_invoices;                             
l_invoices invoices_ntt := invoices_ntt();                     
begin                                                          
l_invoices.extend(3);                                          
l_invoices(1) := invoice_obt(100);                             
l_invoices(2) := invoice_obt(200);                             
l_invoices(3) := invoice_obt(200);                             
l_customer := customer_with_invoices(1,l_invoices);                                                 
end;    

如何使用dbms\U输出打印出l\U客户。