fixup! fix(drand): add null HistoricalBeaconClient for old beacons

chain/beacon/drand/drand.go

@@ -113,6 +113,12 @@ func NewDrandBeacon(genesisTs, interval uint64, ps *pubsub.PubSub, config dtypes
 	} else {
 		log.Info("drand beacon without pubsub")
 		if len(clients) == 0 {
+			// This hack is necessary to convince a drand beacon to start without any clients. For
+			// historical becaons we need them to be able to verify old entries but we don't need to fetch
+			// new ones. With pubsub enabled, it acts as a client so drand is happy, but if we don't have
+			// pubsub then drand will complain about old beacons withotu clients. So we make one that
+			// it'll think is a valid client and that it won't speed test (hence the need to mark it as
+			// as "watcher").
 			historicalClient := &historicalBeaconClient{}
 			clients = append(clients, historicalClient)
 			opts = append(opts, dclient.WithWatcher(func(chainInfo *dchain.Info, cache dclient.Cache) (dclient.Watcher, error) {