@Nullable
  private static DomExtension registerChild(DomExtensionsRegistrar registrar, DomGenericInfo elementInfo, String childName) {
    if (elementInfo.getCollectionChildDescription(childName) == null) { // register if not yet defined statically
      Class<? extends AntDomElement> modelClass = getModelClass(childName);
      if (modelClass == null) {
        modelClass = AntDomElement.class;
      }
      return registrar.registerCollectionChildrenExtension(new XmlName(childName), modelClass);
    }
    return null;
  }
@Nullable
  private static DomExtension registerChild(DomExtensionsRegistrar registrar, DomGenericInfo elementInfo, String childName)