title: Return empty string instead "null" in WCF
body: <p>I have create Wcf service point that returns json.
  And my question is how to return empty string in json instead null.</p>
  
  <pre><code>{
   "Avatar": null // send only -&gt; ""
   "Email": null,
   "FirstName": "John",
   "ID": 1,
   "LastName": "Travolta",
   "NickName": null,
   "Password": null
  }
  </code></pre>
  
  <p>-------EDIT---------</p>
  
  <pre><code>    [DataMember]
      public int ID { get; set; }
  
      [DataMember]
      public string FirstName { get; set; }
  
      [DataMember]
      public string LastName { get; set; }
  
      [DataMember]
      public string NickName { get; set; }
  
      [DataMember]
      public string Email { get { return string.IsNullOrEmpty(_email) ? "" : _email; } set { _email = value; } }
  
      private string _email;
  
      [DataMember]
      public string Password { get; set; }
  
      [DataMember]
      public string Avatar { get; set; }
  </code></pre>