Form Validation validating blank values with min_length and valid_email rules

I need to update database table columns only if valid fields are received in the request.

If a field is received with a blank value '', the validation rules must be applicated or not?

Why is a blank value '' accepted when the min_length[5] (strlen('') equals 0, less then 5) and valid_email ('' is not a valid email address) rules are set?

If proceed the columns will be populated with blank values... But this can not happen!

How to solve this?

Please, check the code:

PHP Code:

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

/**
 * Class Issue
 */
class Issue extends CI_Controller
{

    public function index()
    {
        $this->load->library('form_validation');

        // Test: If you add one character in username or email the validation will run and show the errors...
        $userdata = ['username' => '', 'email' => ''];
        //$userdata = $this->input->post();

        $this->form_validation->set_data($userdata);
        $this->form_validation->set_rules([
            [
                'field' => 'username',
                'label' => 'Username',
                'rules' => 'min_length[5]|max_length[32]',
            ],
            [
                'field' => 'email',
                'label' => 'Email',
                'rules' => 'valid_email',
            ],
        ]);

        if ( ! $this->form_validation->run())
        {
            var_dump($this->form_validation->error_array());
            exit;
        }

        echo 'Validated! Data to be updated: ';
        var_dump($userdata);
    }

} 


I see that  it is intentional. But is correct and I have not understand something?

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