A question about time series graphics

I have a MySQL data source
There are two fields in the dataset: time and value. The time field is discontinuous, such as 202112141516 and 202112141819
When I put the data set into grafana, a straight line is formed between the two on the graph. However, the effect I want is that the value should be 0 or null on the timeline without data
What should I do? Can someone help me?