File upload validation

I have a problem with my file upload validation in CakePHP.

When I add a new record with an image upload field...

• ... image should be required.
• ... image file extension sould be jpg, png or gif.

When I edit an existing record with an image upload field...

• ... image is not required.
• ... when image is choosen: image file extension sould be jpg, png or gif.

Here's my best model code attempt so far:

<?php


class Outlet extends CoasterCmsAppModel
{
    public $validate = array(
        'name' => array(
            'rule' => 'notEmpty', // verplicht
            'message' => 'Name is required.',
            'allowEmpty' => true
        ),
        'intro' => array(
            'rule' => 'notEmpty', // verplicht
            'message' => 'Intro is required.'
        ),
        'photo' => array(
            'validFileSize' => array( // zelf gekozen naam van de regel
                'rule' => array('filesize', '>', 0), // verplicht
                'on' => 'create',
                'message' => 'Photo is required.'
            ),
            'validExtension' => array( // zelf gekozen naam van de regel
                'rule' => array('extension', array('jpg', 'jpeg', 'png', 'gif')),
                'on' => 'create',
                'message' => 'Photo has to contain a valid extension (jpg, jpeg, png or gif).'
            ),
            'validExtension' => array( // zelf gekozen naam van de regel
                'rule' => array('extension', array('jpg', 'jpeg', 'png', 'gif')),
                'allowEmpty' => true,
                'on' => 'update',
                'message' => 'Photo has to contain a valid extension (jpg, jpeg, png or gif).'
            )
        )
    );
   
    public function afterValidate()
    {
        $filename = $this->data['Outlet']['photo']['name'];
       
        if (!empty($filename)) {
            move_uploaded_file($this->data['Outlet']['photo']['tmp_name'], WWW_ROOT . 'img' . DS . 'outlets' . DS . $filename);
           
            $this->set('photo', $filename);
        } else {
            unset($this->data['Outlet']['photo']);
        }
    }
}

The "add" validation works fine for me. But strange as it is, when I edit a record, I keep getting the error message "Photo has to contain a valid extension (jpg, jpeg, png or gif)."

Somebody who can help me out of this? ;)

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