title: Qt QJsonDocument::fromBinaryData() does not work
body: <p>Here is simple code:</p>
  
  <pre><code>QByteArray ba  = jdoc.toBinaryData();
  QJsonDocument jdoc2;
  jdoc2.fromBinaryData(ba);
  qDebug() &lt;&lt; jdoc.isNull();
  qDebug() &lt;&lt; jdoc2.isNull();
  </code></pre>
  
  <p>Result: <code>jdoc</code> is not null, but <code>jdoc2</code> is null. What am I doing wrong? It looks like <code>jdoc2.fromBinaryData(ba);</code> does not work at all.
  I use Qt 5.5.0</p>