User applications are NOT required to call Response::end() after streaming
or sending response data (though it's not incorrect to do so) -- the server
will automatically call end() as needed.
Passing the optional $finalBodyChunk parameter is a shortcut equivalent to
the following:
$response->stream($finalBodyChunk);
$response->end();
Note: Invoking Response::end() with a non-empty $finalBodyChunk parameter
without having previously invoked Response::stream() is equivalent to calling
Response::send($finalBodyChunk).