# Welcome to the Highcharts Maps JS (highmaps) Options Reference

These pages outline the chart configuration options, and the methods and properties of Highcharts objects.

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# series.mapline.dataLabels.nullFormatter

Callback JavaScript function that defines formatting for points with the value of null. Works analogously to formatter. `nullFormatter` can be applied only to series which support displaying null points. `heatmap` and `tilemap` supports `nullFormatter` by default while the following series requires (series.nullInteraction)[#series.nullInteraction] set to `true`: `line`, `spline`, `area`, `area-spline`, `column`, `bar`, and `timeline`. Does not work with series that don't display null points, like `pie`.