docs: protected void checkNotNullAndLength(final Element parent, final String childName, final int minLen, final int maxLen) throws FeedException {
          final Element child = parent.getChild(childName, getFeedNamespace());
          if (child == null) {
              throw new FeedException("Invalid " + getType() + " feed, missing " + parent.getName() + " " + childName);
          }
          checkLength(parent, childName, minLen, maxLen);
      }