itemHeight property
If null, then the menu item heights will vary according to each menu item's intrinsic height.
The default value is _kMinInteractiveDimension, which is also the minimum
height for menu items.
If this value is null and there isn't enough vertical room for the menu,
then the menu's initial scroll offset may not align the selected item with
the popup button. That's because, in this case, the initial scroll
offset is computed as if all of the menu item heights were
_kMinInteractiveDimension.
Implementation
final double? itemHeight;