Upload file without attaching it to a POST

Question

I've brought files with html file field and I'm trying to attach file to wordpress attachments using media_handle_upload

$attach_id = media_handle_upload ( $file_handler, null );

the I've specified second parameter as null because I don't want to attach it with any post, but it returns some WP Error, since it is may be not allowed to media_handle_upload without post id

WP_Error Object
(
    [errors] => Array
        (
            [upload_error] => Array
                (
                    [0] => Array
                        (
                            [0] => 0
                            [1] => 0
                            [2] => 0
                        )

                )

        )

    [error_data] => Array
        (
        )

)

is it possible to upload images with wordpress default without assigning it to any post?