title: IOException: "Received authentication challenge is null" (Apache Harmony/Android)
body: <p>I am trying to send a GET via Android's <strong><code>HttpURLConnection</code></strong> (imported from <strong><code>org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnection</code></strong>), and upon receiving the response, an <strong>IOException</strong> is thrown:</p>
  
  <blockquote>
    <p>in doRequestInternal(): "Received authentication challenge is null"</p>
  </blockquote>
  
  <p>What does this error mean, and what is causing this? I am writing OAuth parameters to the Authorization header, but I do this on other occasions, too, without problems.</p>
  
  <pre><code>    if (connection == null) {
          connection = (HttpURLConnection) new URL(endpointUrl).openConnection();
          connection.setRequestMethod("GET");
      }
  
      //... do some OAuth message signing
  
      connection.connect();
  
      int statusCode = connection.getResponseCode(); // throws IOException
  </code></pre>