Column 'username' cannot be null - codeigniter

Question

I wonder why there is this error message appearing. Column 'username' cannot be null
?
I set Null to No.
A Database Error Occurred
Error Number: 1048
Column 'username' cannot be null
INSERT INTO login (username, email, password, role) VALUES
(NULL, NULL,
'$2y$10$FaVW7V1yEDB0NnlmgwPHQ.SQi34ZCXi9ABJDOebDflZ.cqcSwZAoW', NULL)
Filename: C:/Program
Files/EasyPHP-Devserver-16.1/eds-www/companygiondaci/system/database/DB_driver.php
Line Number: 691
views/addusers.php
<div class="row-fluid">
<div class="span12">
<?php $this->load->library('form_validation'); ?>
<?php echo $successmessage; ?>
<?php echo validation_errors(); ?>
<?php echo form_open('cpages/addusersdb'); ?>
<div class="widget-box">
<div class="widget-title"><h5>Add User</h5></div>
<div class="widget-content">
<table border="0" style="width: 100%; height: 90px;">
<tr>
<td>USERNAME</td>
<td><input type="text" name="username"></td>
</tr>
<tr>
<td>EMAIL</td>
<td><input type="text" name="email"></td>
</tr>
<tr>
<td>PASSWORD</td>
<td><input type="password" name="password"></td>
</tr>
<tr>
<td>ROLE</td>
<td><?php echo form_dropdown('roles', $options, 'administrator'); ?></td>
</tr>
<tr>
<td></td>
<td><input type="submit" class="edit" value="ADD"></td>
</tr>
</table>
</div>
</div>
</div>
</div>
models/Mpages.php
public function add_user()
{
$options = [
'roles' => 'administrator',
];
$hash = password_hash($this->input->post('password'), PASSWORD_BCRYPT, $options);
$data = array(
'username' => $this->input->post('username'),
'email' => $this->input->post('email'),
'password' => $hash,
'role' => $this->input->post('roles')
);
return $this->db->insert('login', $data);
}

Answer 1

if($this->input->post()) {
$hash = password_hash($this->input->post('password'), PASSWORD_BCRYPT, $options);
$data = array(
'username' => $this->input->post('username'),
'email' => $this->input->post('email'),
'password' => $hash,
'role' => $this->input->post('roles')
);
$this->YOUR_MODEL->add_user($data);
}
This should go into your controller.
And your model function should be like this
public function add_user($data)
{
return $this->db->insert('login', $data);
}