Grafana showing dots for elastic search index that has no data

I hope I am asking at the right place. our company uses Grafana to view some time-series data. we have data fed into indices in elastic search head, and then in Grafana we will read those indices.
we have a period when we have no data in elastic search index, but we see dots in Grafana for that period ( those dots has value when you hover the mouse over it in Grafana)

I wonder if anyone has experienced similar issue?