Dart APIunself_componentUnSliverAppBarleading leading property Null safety Widget? leading final Implementation final Widget? leading; unself_component unself_component UnSliverAppBar leading property UnSliverAppBar class Constructors UnSliverAppBar Properties description emoji hashCode implyLeading isCollapseCentered isImmersive key leading runtimeType title trailing Methods createElement createState debugDescribeChildren debugFillProperties noSuchMethod toDiagnosticsNode toString toStringDeep toStringShallow toStringShort Operators operator ==