docs: public static Throwable getOnlyCause(Collection<ErrorMessage> messages) {
      Throwable onlyCause = null;
      for (ErrorMessage message : messages) {
        Throwable messageCause = message.getCause();
        if (messageCause == null) {
          continue;
        }
  
        if (onlyCause != null) {
          return null;
        }
  
        onlyCause = messageCause;
      }
  
      return onlyCause;
    }