static ObjectReader<?> registerIfAbsent(Type type, ObjectReader<?> objectReader) {
        return JSONFactory.getDefaultObjectReaderProvider().registerIfAbsent(type, objectReader);
    }
Register if absent an {@link ObjectReader} for {@link Type} in default {@link com.alibaba.fastjson2.reader.ObjectReaderProvider}

@see JSONFactory#getDefaultObjectReaderProvider()
@see com.alibaba.fastjson2.reader.ObjectReaderProvider#registerIfAbsent(Type, ObjectReader)
@since 2.0.6
core/src/main/java/com/alibaba/fastjson2/JSON.java