@NonNull
  private static List<String> getMutableSingletonList(String msg) {
    ArrayList<String> strings = new ArrayList<>();
    strings.add(msg);
    return strings;
  }
Attempts to validate the provided RetryStrategy. If valid, null is returned. Otherwise a list
of errors will be returned.
jobdispatcher/src/main/java/com/firebase/jobdispatcher/DefaultJobValidator.java