Undefined index: slideimageall

Sometimes (but not everytime) the widget loads, I get this error:

Notice: Undefined index: slideimageall in <path>/wp-content/plugins/wp-image-refresh/functions.php on line 146

I have bracketed the code around that section of code as follows and have not seen the error recur (and the widget seems to work):

    if (isset($_SESSION['slideimageall'])) {    
 
    	if (count($_SESSION['slideimageall']) == 0) {
            $images = $wpdb->get_results("SELECT slideTitle,slideImage,slideText FROM $table_name ORDER BY rand()", OBJECT);

            //Hold complete Image array
            $_SESSION['slideimageall'] = array();

            foreach ($images as $images1) {
                array_push($_SESSION['slideimageall'], array('slideImage' => $images1->slideImage, 'slideTitle' => $images1->slideTitle, 'slideText' => $images1->slideText));
            }
        }    
    }

I don’t know what this will break. Is this a bug?