Response can't send() automic where setJsonContent() method is called

in my Micro App，

use middleware “after”，like below:

<?php
......
$app->after(function () use ($app) {
    $result = $app->getReturnedValue();

    if(is_array($result) || is_object($result)){
        $app->response->setJsonContent($result, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
        // must add this line
        $app->response->send();
    } else {
        $app->response->setContent($result);    
    }
});
...

....
$app->handle();
?>

when my response setJsonContent()，the response must be "$app->response->send()" manual。 but when response setContent() ，it does not need use "$response->send()" method.

is it a bug?