File Upload Conditional

I have an html form with some text and file inputs that submits to a PHP page. I want to error check the image file input but only if they choose to include one. Is there a way to check if there's an uploaded image file? I included my attempt below but it doesn't seem to be working.

if ($_FILES['image'])
{ 
    if ($_FILES['image']['error'] > 0)
    {
        echo 'Problem: '; }}
        switch ($_FILES['image']['error'])
        {
            case 1: echo 'File exceeded upload_max_filesize.';
                break;
            case 2: echo 'File exceeded max_file_size.';
                break:
            case 3: echo 'File only partially uploaded.';
                break;
            case 4: echo 'No file uploaded.';
                break;
            default: echo 'cannot upload.';
                break;
        } 
        exit;
    }
}