DomExtension (final DomExtender extender) { if (myUserMap == null || !myUserMap.containsKey(DOM_EXTENDER_KEY)) { putUserData(DOM_EXTENDER_KEY, new SmartList<>()); } //noinspection unchecked ((List<DomExtender<?>>)myUserMap.get(DOM_EXTENDER_KEY)).add(extender); return this; }