title: Issues Converting String to javax.json.JsonString
body: <p>I have a class that looks something like this</p>
  
  <pre><code>    private byte[] profilePicture;
      private ProfileType profileType;
      private String profileHandle;
      private String personalEmail;
      private Address address;    
  </code></pre>
  
  <p>To convert this to Json using javax.json is like this:</p>
  
  <pre><code>    JsonObject payloadObject = Json.createObjectBuilder()
      .add("profilePicture", profilePictureEncoded)
      .add("profileType", profileType.ordinal())
      .add("profileHandle", profileHandle)
      .add("personalEmail", personalEmail)
      .add("webAppEmail", webappEmail)
      .add("address", address.produceJsonPayload())
      .build();
  </code></pre>
  
  <p>All good!! except sometimes there is no profile picture so I wanted to build this incrementally ie</p>
  
  <pre><code>    JsonObject payloadObject = Json.createObjectBuilder().build();
      if(profilePicture != null)
      {
          final String profilePictureEncoded = ..... //encode the image
          payloadObject.put("profilePicture",profilePictureEncoded);
      }
  </code></pre>
  
  <p>problem is you cant because I can't cast profilePictureEncoded to a JsonString</p>
  
  <p>Has anyone got something like this working?  Or do I need to use another Json Library?</p>
  
  <p>Damien </p>