Hello,
on a page, i have : 
if (!empty($_FILES['logo']['name'])) {
        $dossier = 'upload/';
        $fichier = basename($_FILES['logo']['name']);
        $taille_maxi = 100000;
        $taille = filesize($_FILES['logo']['tmp_name']);
        $extensions = array('.png', '.jpg', '.jpeg');
        $extension = strrchr($_FILES['logo']['name'], '.'); 
        //Début des vérifications de sécurité...
        if(!in_array($extension, $extensions)) 
        {
             $erreur = 'ERROR you  must upload the right type';
        }
        if($taille>$taille_maxi)
        {
             $erreur = 'too heavy';
        }
        if(!empty($erreur)) 
        {
                   .......................
        }
The problem is, if the users wants to edit information WITHOUT uploading a LOGO, it raises an error : 'error you must upload the right type'
So, if a user didn't put anything in the inputbox in order to upload it, i don't want to enter in these conditions test.
i tested :
if (!empty($_FILES['logo']['name']) and if (isset($_FILES['logo']['name'])
but both doesn't seems to work.
Any ideas? 
thanks.