Reset axisLabelFormatter to default

[btilongnguyen]

Hi. I saw there is an axisLabelFormatter option here to format the tick values that appear along an axis.
It works just fine, however, I am wondering if there is a way to reset that option (go back to use the default formatter of Dygraphs) once I set it previously.
I tried to set axisLabelFormatter to undefined or null but got this error in the console.

Uncaught TypeError: Cannot read properties of undefined (reading 'call')
    at getDateAxis (vendor.js:419283)
    at dateTicker (vendor.js:418918)
    at Dygraph.push.10681.Dygraph.addXTicks_ (vendor.js:422821)
    at Dygraph.push.10681.Dygraph.drawGraph_ (vendor.js:423184)
    at Dygraph.push.10681.Dygraph.predraw_ (vendor.js:422901)
    at Dygraph.push.10681.Dygraph.resize (vendor.js:424139)
    at resizeHandler_ (vendor.js:421653)
    at ZoneDelegate.invokeTask (polyfills.js:668)
    at Zone.runTask (polyfills.js:356)
    at ZoneTask.invokeTask [as invoke] (polyfills.js:820)

Any suggestion? Thank you.