DataFrame with `Nothing?` column is detected as `FormattedFrame<*>?` in notebooks

[Jolanrensen]

As reported here: https://kotlinlang.slack.com/archives/C05333T208Y/p1762352545398199

This is the direct result of hasFormattedColumns():

internal fun AnyFrame.hasFormattedColumns() =
    this.getColumns { colsAtAnyDepth().colsOf<FormattedFrame<*>?>() }.isNotEmpty()

As colsOf<T>() includes all subtypes of T, colsOf<FormattedFrame<*>>()? will include null filled columns, of type Nothing?. This behavior is correct, though in hasFormattedColumns() this causes a problem, as it will return true if the dataframe has a Nothing? column.

Let's check the library for other colsOf<.*?>() usages to prevent similar issues.

[ileasile]

Please check such DF in the notebook after fix - it's important that it's rendered fine when it's not considered formatted

[Jolanrensen]

While in most cases, the potential Nothing? column is handled well, it can still show up unexpected in some cases, like:

or

btw, this is a weird bug too actually, you should be able to put any instance in a Nothing column

Edit: no, it actually isn't. fillNulls {} uses update {} which doesn't allow changing types of columns. fillNulls { nothing? } simply doesn't make sense as there's nothing you can fill it up with without changing the type.