I think I solved my problem, comment out the following codes in "UploadHandler.php".
protected function get_file_objects($iteration_method = 'get_file_object') {
$upload_dir = $this->get_upload_path();
if (!is_dir($upload_dir)) {
return array();
}
return array_values(array_filter(array_map(
array($this, $iteration_method),
scandir($upload_dir)
)));
}
By doing this, you won't get any file lists after refreshing the page or running $("table tbody.files").empty();
manually.