java.sql.date insert as null

Hello,

How can I store a java.sql.date as null in database. The problem is
(pseudecode):
....
java.sql.Date date = null;
....
Customer cust = new Customer(id);
cust.setSqlDate(date);

..insert into Customer (id..,date,...)
values(...
...." ' "+in.getSqlDate()+" ' ".....
...)

then the exception

java.sql.SQLException: ERROR: invalid input syntax for type date: "null"
........

when I select a row with empty date and system.out.print, it  gives me a
null.. but why I can't store it as null
I use jdbc3, postgresql 8.0.1 and java 5 (tiger) on windows

thank you

best regards Mican Bican