Create an empty record

Hi

How would one goabout creating an empty record (for use in relations).

Eg
create table product(
	productid	SERIAL NOT NULL,
	product	TEXT,
	PRIMARY KEY(productid)
);

create table product_billable(
	productid	INT4 NOT NULL,
	billaddress	TEXT,
	PRIMARY KEY (productid),
	FOREIGN KEY (productid) REFERENES product(productid) ON DELETE CASCADE
);

All fields except for the primary key can be NULL.

What if I wanted to add a new billable product but I have not got a name 
for it yet?

So how could I insert a new record in product that can be used in 
product_billable?

I have tried INSERT INTO product() VALUES(); but as expected it did not 
work.

All help appreciated
Best regards
Per-Olof Pettersson