code: public void addPayload(final Payload payload) {
  		ApptentiveLog.v(PAYLOADS, "Adding payload: %s", payload);
  		singleThreadExecutor.execute(new Runnable() {
  			@Override
  			public void run() {
  				try {
  					dbHelper.addPayload(payload);
  					sendNextPayloadSync();
  				} catch (Exception e) {
  					ApptentiveLog.e(PAYLOADS, e, "Exception while adding a payload: %s", payload);
  					logException(e);
  				}
  			}
  		});
  	}
docs: If an item with the same nonce as an item passed in already exists, it is overwritten by the item. Otherwise
  a new message is added.