Form Validation validating blank values with min_length and valid_email rules

The easiest thing is to add required to the set of rules.

PHP Code:

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