private void insertCustomAlert() {
        switch (customAlert.size()) {
            case 0:
                aps.remove("alert");
                break;
            case 1:
                if (customAlert.containsKey("body")) {
                    aps.put("alert", customAlert.get("body"));
                    break;
                }
                // else follow through
                //$FALL-THROUGH$
            default:
                aps.put("alert", customAlert);
        }
    }
Returns the JSON String representation of the payload
according to Apple APNS specification

@return  the String representation as expected by Apple
src/main/java/com/notnoop/apns/PayloadBuilder.java