return 404 from Async Task
<p>I have this method in my mvc controller:</p>

<pre><code>public ActionResult BlaBla()
{
    if (!ModelState.IsValid)
        return new HttpNotFoundResult();

    // ...
}
</code></pre>

<p>I want to create an Async version of it. So, I thought to change the code like this:</p>

<pre><code>public async Task&lt;ActionResult&gt; BlaBla()
{
    if (!ModelState.IsValid)
        return new HttpNotFoundResult(); // Compiling error: this line is not working

    // ...
}
</code></pre>

<p>My question is how to return error codes (404, 500, ...) from my mvc controller, when using <code>async Task&lt;...&gt;</code> style?</p>