Avoid crash if accountmanager not configured.

CHANGELOG.md

@@ -1,4 +1,5 @@
 Development
+  - avoid crash if accountmanager not configured
   - avoid crash if beacon committee subscription information is not present
   - add measurement of validator status fetching operations
   - increase maximum block receipt delay metric from 4s to 12s

main.go

@@ -553,9 +553,10 @@ func startAccountManager(ctx context.Context, monitor metrics.Service, eth2Clien
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to start wallet account manager service")
 		}
+		return accountManager, nil
 	}
 
-	return accountManager, nil
+	return nil, errors.New("no account manager defined")
 }
 
 func selectBeaconBlockProposalProvider(ctx context.Context,