title: apex:commandButton can't return nothing?
body: <p>I have:</p>
  
  <pre><code>&lt;apex:commandButton action="{!whatever}" value="myButton" reRender="sectionX" /&gt;
  </code></pre>
  
  <p>And</p>
  
  <pre><code>public String whatever(){
      return 'ok';
  }
  </code></pre>
  
  <p>It doesn't work (returns 401 Unauthorized), but if I write:</p>
  
  <pre><code>public void whatever(){
      // some code
  }
  </code></pre>
  
  <p>works fine.</p>
  
  <p>The question is: how can I return something (a JSON or a Page) to this call?</p>
  
  <p>Thanks</p>