The chartview does not have any API to control the behavior of the empty values. We only support the gap mode, where a gap is left where there are empty values. You can create a second series for which you will need to calculate these interpolated values. You can have that series with a different look (say dash array) so that it is obvious that these values are somehow different. Consider also including a legend, so that the person reading this chart knows that these are indeed empty/missing/interpolated values.
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