$this->db->get_where

 Hi, Good day.

I found this thing by mistake.
1) Controller Function

Code:

        $id = trim($this->input->post('id'));
        $pw = md5(trim($this->input->post('pwd')));

        $queryResult = $this->userinfo_model->login_user($id, $pw);

2) Model Function

Code:

$query = $this->db->get_where('userinfo', array('id' => $id, 'password' => $pw));

What I found:
a) When $pw is null
Supposed SQL should be:

Code:

select * from userinfo where id = '$id' and password is null;

But the actual SQL is like:

Code:

select * from userinfo where id = '$id';

Is this an issue or I made any mistake??
Thanks