Help Column cannot be null

Hello guys i just need your help about my form having error submitting it

Column 'date' cannot be null

and here's my code:

PHP Code:

public function create_purchase(){

        $data_list = array(

            'sup_name' => $this->input->post('sup_name'),
            'qty' => $this->input->post('qty'),
            'price' => $this->input->post('price'),
            'date_expired' => $this->input->post('date_expired'),
            'date' => $this->input->post('date')
            );

        $this->model_products->add_purchase($data_list);
        $this->session->set_flashdata('success', 'Successfully Add!');
        redirect('admin/purchase', 'refresh');
    } 


Model

PHP Code:

public function add_purchase($data_list){

        
        if($this->db->insert('purchases', $data_list)){
            return TRUE;
        }else{
            return FALSE;
        }
    } 


Database Table

PHP Code:

CREATE TABLE `purchases` (
`purchase_id` int(11) NOT NULL AUTO_INCREMENT,
`sup_name` varchar(50) NOT NULL DEFAULT '',
`date` date NOT NULL DEFAULT '',
`qty` int(11) NOT NULL DEFAULT '',
`price` decimal(12,2) NOT NULL DEFAULT '',
`date_expired` date NOT NULL DEFAULT '',

// Others 


Hope you can help me. Thanks!