Why am I not getting enough value error since I am using auto increment and not adding any value in the insert?

```
CREATE TABLE Customer(
customerId INTEGER GENERATED ALWAYS as IDENTITY(START with 1 INCREMENT by 1) primary key,
firstName VARCHAR2(25) not null,
middleName VARCHAR2(25),
lastName VARCHAR2(25) not null,
dateOfBirth DATE not null,
phoneNumber NUMBER(10) not null,
billingAddress VARCHAR2(35) not null
);

INSERT INTO Customer VALUES
('Sam', null, 'Siqi', (TO_DATE('18/12/1999', 'DD/MM/YYYY')),12345678, 
'Smith Street NSW');

```