Incorrect value in Grafana for days when value is missing in Prometheus

I am using grafana to show some metrics about my app. For example, I calculated values for a metric named session_count from 2023-01-01 to 2024-01-07. Then I fed them into promethues with the following format:

# TYPE session_count gauge
session_count{date="2023-01-01"} 99 1672540200
session_count{date="2023-01-02"} 692 1672626600
session_count{date="2024-01-01"} 3802 1704076200
session_count{date="2024-01-02"} 2810 1704162600
session_count{date="2024-01-03"} 2870 1704249000
session_count{date="2024-01-04"} 1155 1704335400
session_count{date="2024-01-05"} 832 1704421800
session_count{date="2024-01-06"} 3476 1704508200
session_count{date="2024-01-07"} 3276 1704594600

Then I add some chart into my grafana dashboard to show this metric. After a couple of days, I realized even I didn’t send any new data, It still shows a number for this metric!

When I checked prometheus, there is no problem at all, and the last metric value corresponds to 2024-01-07.

I did another test outside the dashboard and the result was strange.

I do not understand what this chart means. I am new to Grafana.

Does anyone know what is the cause of this problem? I just wanted to display a series of daily statistics with Grafana, but there seems to be a problem. I saw a similar problem in another dashboard. My metric did not have a value for a specific day, but Grafana showed the previous day’s value for that day, which is wrong. Do you have a suggestion to fix this problem?