Change invalid axisX title config property from false to null (#4881)
Change invalid axisX title config property from false to null (#4881)


uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite