title: SyntaxError: JSON.parse: unexpected end of data
body: <p>I try add data to database using ajax. I prepare data: </p>
  
  <pre><code>$(".panel").on('click','.buttons_save',function() {
      groupIdD = this.id;
      groupNameD=$("#groupName").val();
      groupDescriptionD=$("#groupDescription").val();
      paramGroupD=$("#paramGroup").val();
      paramOrderD=$("#paramOrder").val();
  
      $.ajax({
          dataType: "json",
          type: "POST",
          url: ajaxSetGroupParams,
          data: { 
              groupId: groupIdD,
              paramGroup: groupNameD,
              groupName: groupDescriptionD,
              groupDescription: paramGroupD,
              paramOrder: paramOrderD
          }
      })
  
      .done(function() {
          alert( "success" );
      })
      .fail(function(XMLHttpRequest, textStatus, errorThrown) {
          console.log(XMLHttpRequest);
          console.log(textStatus);
          console.log(errorThrown);
      })
  
  
  });
  </code></pre>
  
  <p>And I add this data to database (everything is ok, data are add to database).
  $polaczenie_z_baza=$_SESSION['db']['connectObjs']['system'];</p>
  
  <pre><code>$id_group=$_REQUEST['groupId'];
  $paramGroup=$_REQUEST['paramGroup'];
  $groupName=$_REQUEST['groupName'];
  $groupDescription=$_REQUEST['groupDescription'];
  if (isset($_REQUEST['paramOrder'])) {
      $paramOrder=$_REQUEST['paramOrder'];
  }
  else {
      $paramOrder=0;
  }
  
  $qUpdateData    = '
  UPDATE
  `grupy_parametrow_konfiguracyjnych`
  SET
  `id_grupa_nadrzedna` ='.$paramGroup.',
  `nazwa_grupy` = '.$groupName.',
  `opis_grupy` = '.$groupDescription.',
  `kolejnosc` ='.$paramOrder.'
  WHERE
  `id_grupa_parametrow` = '.$id_group; 
  
  $result = stdIUDQuery( $qUpdateData, $polaczenie_z_baza);
  </code></pre>
  
  <p>But always I have fail information: </p>
  
  <pre><code>parsererror
  SyntaxError: JSON.parse: unexpected end of data
  
  return window.JSON.parse( data );
  </code></pre>