Stacked graph not properly handling null values

[ischolten]

Filing a bug report? Please include the following:

Currently I have two series of data that I am displaying as a stacked line graph. The data looks similar to this:
[[null, null],
[1, null],
[null, null],
[null, 1],
[1, null],
[null, 1],
[null, 1],
[null, 1]]

where the first value represents one series and the second value represents another. Currently the graph looks like the following when stackGraph is true.

I would expect that the second(orange) series would move down and show at value 1 on the y axis since the first series had no values at that point.

2. Browser and Operating System that exhibit the problem
   Currently using Chrome.

3. Version of dygraphs that you're using: 2.1.0

[mirabilos]

Does it work as expected if you use NaN instead of null? See https://dygraphs.com/data.html#array