nullJsonProperty
fun <T : CSJsonObjectStore> CSStore.nullJsonProperty(key: String, type: KClass<T>, default: T? = null, onChange: ArgFun<T?>? = null): CSStoreProperty<T?>
inline fun <T : CSJsonObjectStore> CSStore.nullJsonProperty(key: String, default: T? = null, noinline onChange: ArgFun<T?>? = null): CSStoreProperty<T?>