บันทึกข้อมูลไม่ได้ กรณีไม่ได้แนบไฟล์ คำสั่ง PATHINFO_EXTENSION

if(isset($_POST['save']))
{
    $filename = $_FILES['myfile']['name'];

    $destination = 'uploads/' . $filename;
    
    $extension = pathinfo($filename,PATHINFO_EXTENSION);
    
    $file = $_FILES['myfile']['tmp_name'];
    $size = $_FILES['myfile']['size'];
if(!in_array ($extension,['zip','pdf','png','txt']))
{
    echo"Your file extension must be zip,pdf,png,txt";
}
elseif($_FILES['myfile']['size'] > 100000000)
{
    echo "file is too large" ;
}