code: public static XMLStreamException missingRequired(final XMLExtendedStreamReader reader, final String... required) {
          final StringBuilder b = new StringBuilder();
          for (int i = 0; i < required.length; i++) {
              final String o = required[i];
              b.append(o);
              if (required.length > i + 1) {
                  b.append(", ");
              }
          }
  
          return wrapMissingRequiredAttribute(ControllerLogger.ROOT_LOGGER.missingRequiredAttributes(b, reader.getLocation()),
                                              reader, new HashSet<>(Arrays.asList(required)));
      }
docs: Get an exception reporting a missing, required XML attribute.
  @param reader the stream reader
  @param required a set of enums whose toString method returns the
  attribute name
  @return the exception