title: Why does Qt reject a valid JSON?
body: <p>Using Qt-5.0, I have this JSON string</p>
  
  <pre><code>{"type":"FILE"}
  </code></pre>
  
  <p>I expected that <code>fromBinaryData</code> accept <code>.toLocal8Bit()</code> of the string as a valid format but it doesn't. </p>
  
  <pre><code>QString j = "{\"type\":\"FILE\"}";
  
  auto doc = QJsonDocument::fromBinaryData(j.toLocal8Bit());
  
  doc.isNull() // It's true, means the entry is not valid
  </code></pre>
  
  <p>Did I miss something?</p>