All of ThemeData's factory constructor parameters should be required to be non-null

[HansMuller]

Because having a few needless exceptions is confusing and likely due to historical accident not design.

Of the 73 ThemeData.raw() parameters, buttonColor, applyElevationOverlayColor, and cupertinoOverrideTheme are not required to be non-null.

[markusaksli-nc]

Currently the only two remaining properties that are not required to be non-null are cupertinoOverrideTheme and androidOverscrollIndicator. androidOverscrollIndicator defaults to AndroidOverscrollIndicator.glow so it seemed like it wouldn't be that hard to change but I ran into a failing test because of this null dependent behavior

flutter/packages/flutter/lib/src/material/app.dart

Lines 781 to 783 in 5840db7

	final AndroidOverscrollIndicator indicator = _androidOverscrollIndicator
	?? Theme.of(context).androidOverscrollIndicator
	?? androidOverscrollIndicator;

It seems like this can be circumvented by allowing the ScrollBehavior.androidOverscrollIndicator to be null instead of the ThemeData property but not sure if this would result in a breaking change.