Merge branch 'v5.1.0+' into v5.1.2+

@@ -254,7 +254,7 @@ class _BookInfoPageState extends State<BookInfoPage> {
     if (itemModel != null) {
       lat = itemModel.data.lat;
       long = itemModel.data.long;
-      address = itemModel.data.mapAddress + itemModel.data.realAddress;
+      address = itemModel.data.mapAddress??'' + itemModel.data.realAddress??'';
       setState(() {});
       // _introductionController.text = itemModel.data.sellerdesc;