class FastjsonKeyConvertor implements Function<Object, Object> {

    public static final FastjsonKeyConvertor INSTANCE = new FastjsonKeyConvertor();

    @Override
    public Object apply(Object originalKey) {<FILL_FUNCTION_BODY>}

}

        if (originalKey == null) {
            return null;
        }
        if (originalKey instanceof String) {
            return originalKey;
        }
        return JSON.toJSONString(originalKey);
    
<no_super_class>