Dart APIunself_componentFloatScaffoldmiddle middle property Null safety Widget? middle final Implementation final Widget? middle; unself_component unself_component FloatScaffold middle property FloatScaffold class Constructors FloatScaffold Properties hashCode key leading middle runtimeType trailing Methods build createElement debugDescribeChildren debugFillProperties noSuchMethod toDiagnosticsNode toString toStringDeep toStringShallow toStringShort Operators operator ==