preferred combiner fixed in client cmd (#683)

fedn/cli/client_cmd.py

@@ -79,7 +79,7 @@ def list_clients(ctx, protocol: str, host: str, port: str, token: str = None, n_
 @click.option("-s", "--secure", required=False, default=False)
 @click.option("-pc", "--preshared-cert", required=False, default=False)
 @click.option("-v", "--verify", is_flag=True, help="Verify SSL/TLS for REST service")
-@click.option("-c", "--preferred-combiner", type=str,required=False, default="combiner",help="name of the preferred combiner")
+@click.option("-c", "--preferred-combiner", type=str,required=False, default="",help="name of the preferred combiner")
 @click.option("-va", "--validator", required=False, default=True)
 @click.option("-tr", "--trainer", required=False, default=True)
 @click.option("-in", "--init", required=False, default=None, help="Set to a filename to (re)init client from file state.")