Aggregate function not parallelizable ?

Hello, I'm trying to use timescaledb continuous aggregation with HLL on my database in postgresql 12.7:
```
\dxe

Nom | Version | Schéma | Description
-------------+---------+------------+-------------------------------------------------------------------
hll | 2.15 | public | type for storing hyperloglog data
plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language
timescaledb | 2.3.0 | public | Enables scalable inserts and complex queries for time-series data
```

```sql
CREATE MATERIALIZED VIEW sentdata_summary_daily
WITH (timescaledb.continuous) AS
SELECT network,
time_bucket(INTERVAL '1 day', date) AS bucket,
HLL_ADD_AGG(HLL_HASH_BIGINT(userid)) as users_set
FROM dataselectvol
GROUP BY network,bucket;
ERROR: aggregates which are not parallelizable are not supported
```

But I thought from #73 that HLL functions were parallelisable.

Can you confirm that #73 is fixed in version 2.15 ? Do you think that the issue might be related to TimescaleDB ? Or am I misusing the hll_* functions ?