docs: private static XMLStreamException missingRequiredElement(final XMLStreamReader reader, final Set<?> required) {
          final StringBuilder builder = new StringBuilder();
          Iterator<?> iterator = required.iterator();
          while (iterator.hasNext()) {
              final Object o = iterator.next();
              builder.append(o.toString());
              if (iterator.hasNext()) {
                  builder.append(", ");
              }
          }
          return SecurityManagerLogger.ROOT_LOGGER.missingRequiredElements(builder, reader.getLocation());
      }