private @Nullable XmlContentDFAImpl getNextSubGroup() {
    List<XmlElementsGroup> subGroups = myGroup.getSubGroups();
    int i = subGroups.indexOf(myLastChild.myGroup) + 1;
    return i == subGroups.size() ? null : new XmlContentDFAImpl(subGroups.get(i));
  }
private @Nullable XmlContentDFAImpl getNextSubGroup()