Adding new alerts doesn't work

[Slach]

Tested it and it was works week ago

I tried make following actions sequence
Main menu -> Alert rules -> Add new rule

Choose clickhouse as datasource
choose Column timestamp type -> DateTime
select Database, Table and Timestamp column

press Go to query

and got wrong structure passed to EvalQuery, changed from String to Object

it was always string, not the object

look to
https://github.com/Altinity/clickhouse-grafana/blob/master/docker/grafana/dashboards/array_join_nested.json#L112
for example