How to prevent Sequelize from inserting NULL for primary keys with Postgres-open source projects sequelize/sequelize

I have created a table in postgresql 9

create table stillbirth(id serial primary key, state varchar(100), count int not null, year int not null); 

trying to write a sample on node.js with sequelize 1.4.1 version.

mapped the above table as

var StillBirth = sequelize.define('stillbirth',
{ id: {type: Sequelize.INTEGER, primaryKey: true, autoIncrement: true},
state: Sequelize.STRING,
year: Sequelize.INTEGER,
count: Sequelize.INTEGER
}, {timestamps: false, freezeTableName: true});

now when i try to create a new instance of Stillbirth and save it, i get errors.

/** new instance create code **/

StillBirth
   .build({state: objs[j].state, year: objs[j].year, count: objs[j].count})
   .save()
   .error(function(row){
         console.log('could not save the row ' + JSON.stringify(row));
        })
   .success(function(row){
       console.log('successfully saved ' + JSON.stringify(row));
   })

error i get

*Executing: INSERT INTO “stillbirth” (“state”,”year”,”count”,”id”) VALUES (‘Andhra Pradesh’,2004,11,NULL) RETURNING ; could not save the row {“length”:110,”name”:”error”,”severity”:”ERROR”,”code”:”23502″,”file”:”execMain.c”,”line”:”1359″,”routine”:”ExecConstraints”}

If you look at the sql that its generating, it puts null for the primary key which should ideally be generated by the db.

Can someone help me as to what am i missing here ?