Issue on null values


I have two different cpu runs like below.
run 1 : 8:00 AM to 8:45 AM (values)
run 2 : 8:00 AM to 8:30 AM (values) and from 8:30 to 8:45 (all null values. that means run stooped at 8:30)

So i want run 1 should plot till 8:45 and run 2 should plot till 8:30 on same graph. but it is showing error

I tried update nulls with zero for “run 2” from 8:30 to 8:45 . Now it is plotting values for both runs . But I can see plotting on line on zero for x-axis for “run-2” after 8:30 onwards.

how to plotting my run -2 values till 8:30?

Any suggestion on this?