Too few arguments, 0 passed - php

Question

I'm currently in an intership for a restaurant. I'm coding a website for them and I'm starting the CRUD on it.
The problem is that no data is passed to the controller, and so it doesn't update the drink.
Hope someone can help me.
I use a form to update a drink, here it is.
<div class="col-lg-6 order-lg-2">
<div class="p-5">
<p>Veuillez renseigner tous les champs !</p>
<p>Si un champ ne change pas, copier-coller ce champ depuis le tableau juste au-dessus.</p>
<form action="<?php base_url().'index.php/boissons/resp_modif_boisson/'.$son['id_boisson'] ?>" method="post">
<div class="form-group">
<label for="nom">Nom :</label>
<input type="text" class="form-control" id="nom" name="nom" maxlength="60" required>
</div>
<div class="form-group">
<label for="desc">Descriptif :</label>
<input type="text" class="form-control" id="desc" name="desc" maxlength="500" required>
</div>
<div class="form-group">
<label for="prix">Prix :</label>
<details>Si prix décimal, utilisez le "." ! (exemple : 1.99)</details>
<br>
<input type="number" class="form-control" id="prix" name="prix" min="0" step="0.01" value="0.00" required>
</div>
<button type="submit" class="btn btn-warning">Modifier</button>
</form>
</div>
</div>
And here is the controller.
public function resp_modif_boisson($num){
$this->load->helper('form');
$this->load->library('form_validation');
if($this->session->statut=="R"){
$this->form_validation->set_rules('nom', 'nom', 'required');
$this->form_validation->set_rules('desc', 'desc', 'required');
$this->form_validation->set_rules('prix', 'prix', 'required');
$nom = htmlspecialchars(addslashes($this->input->post('nom')));
$desc = htmlspecialchars(addslashes($this->input->post('desc')));
$prix = htmlspecialchars(addslashes($this->input->post('prix')));
var_dump($nom);
var_dump($desc);
var_dump($prix);
echo "test";
if ($this->form_validation->run() == FALSE){
$data['boi'] = $this->db_model->get_boisson($num);
echo "false";
$this->load->view('templates/haut_administrateur.php');
$this->load->view('resp_modif_boisson',$data);
$this->load->view('templates/bas');
}else{
$this->db_model->modif_boisson($num, $nom, $desc, $prix);
$data['boi'] = $this->db_model->get_boisson($num);
echo "true";
$this->load->view('templates/haut_administrateur.php');
$this->load->view('resp_modif_boisson',$data);
$this->load->view('templates/bas.php');
}
}else{
$data['boi'] = $this->db_model->get_all_boissons();
$this->load->view('templates/haut_accueil.php');
$this->load->view('boissons_afficher',$data);
$this->load->view('templates/bas.php');
}
}