Wow, interesting question.
Not sure how using the default LineChart.
Maybe you could seperate points using the "null" value and add them to the dataProvier(is it ArrayCollection)?
I don't even know if this is gonna work.
I already have ArrayCollection with each second null data
Not exactly sure what you're trying to do from the initial post. A line series will handle null or 'NaN' values. If you don't want the line to break, you should clean your data source (Array collection) prior to setting it as the dataprovider for the line series. You can either interpolate the values using whatever interpolation technique you see fit, if this is applicable to your project, or you can remove them entirely and allow flex to do the interpolation in drawing the line.
I have array collection with two data for each elements, first I use for first lineseries, second for second . And only one have each second data - null
I fixed it . I override update filter for lineSeries . it work wrong for my data