[Bug] Multichart points with y: null render as y: 0

[dinkom]

NVD3 version used: 1.8.6

Browser and OS used: Chrome 67 on Mac

Live Example: https://jsfiddle.net/Ldbjvm8c/8/

Expected Behaviour:
null values of y should not be rendered at all (like when using just a line chart, not a multi chart).

Present Behaviour:
null values of y rendered as zeros.

Any more information regarding the issue:
On top of null values being rendered as zeros, they don't connect as 'real' data points connect in a line chart (with the line itself), they just appear as single dots.