提交：修改判断条件；

lib/widget/state_layout.dart

@@ -63,7 +63,7 @@ class _StateLayoutState extends State<StateLayout> {
       mainAxisAlignment: MainAxisAlignment.center,
       children: <Widget>[
         Offstage(
-          offstage: widget.img!.isEmpty,
+          offstage: img.isEmpty,
           child: Opacity(
             opacity: 1,
             child: Container(