code: public JSONObject putOnce(Enum<?> key, Object value) throws JSONException {
  		return putOnce(key.name(), value);
  	}
docs: Put a key/value pair in the JSONObject, but only if the key and the value
  are both non-null, and only if there is not already a member with that
  name.
  
  @param key
  @param value
  @return his.
  @throws JSONException
  if the key is a duplicate