title: How to judge the node of json exists
body: <p>I am using Newtonsoft.Json to Deserialize json string to Object, but I can't judge if the node is <code>null</code> or not. eg. <code>jo["data"]["prevtime"]</code>, sometimes <code>json</code> has the node of <code>["prevtime"]</code>, sometimes doesn't have <code>["prevtime"]</code>. If <code>["prevtime"]</code> is <code>null</code>, it will report an error.</p>
  
  <pre><code>var jo = JObject.Parse(content);
  if (jo["data"].ToString() == "")
      return new StatusCollection();
  
  var jInfo = jo["data"]["info"];
  StatusCollection list = new StatusCollection();
  Status status = null;
  
  if (jInfo != null)
  {
      foreach (var j in jInfo.Children())
      {
  
         if (jo["data"]["prevtime"] != null) 
         {
             status.Nexttime = jo["data"]["nexttime"].ToString();
             status.Prevtime = jo["data"]["prevtime"].ToString();
         }
  
         status = j.ToObject&lt;Status&gt;();
         if (!string.IsNullOrEmpty(status.Head))
         {
             status.Head += "/50";
         }
         if (!string.IsNullOrEmpty(status.From))
         {
             status.From = "来自" + status.From;
         }
         list.Add(status);
      }
  }
  </code></pre>