code: private CmsUUID readOptionalUUID(JSONObject json, String key) {
  
          String id = readOptionalString(json, key, null);
          if (null != id) {
              try {
                  CmsUUID uuid = CmsUUID.valueOf(id);
                  return uuid;
              } catch (NumberFormatException e) {
                  LOG.debug("Reading optional UUID failed. Could not convert \"" + id + "\" to a valid UUID.");
              }
          }
          return null;
      }
docs: Read an optional uuid stored as JSON string.
  @param json the JSON object to readfrom.
  @param key the key for the UUID in the provided JSON object.
  @return the uuid, or <code>null</code> if the uuid can not be read.