fix flagdecoration

example/lib/main.dart

@@ -118,8 +118,9 @@ class _MyAppState extends State<MyApp> {
                 favorite: ['+39', 'FR'],
                 countryFilter: ['IT', 'FR'],
                 // flag can be styled with BoxDecoration's `borderRadius` and `shape` fields
-                flagDecoration:
+                flagDecoration: BoxDecoration(
-                    BoxDecoration(borderRadius: BorderRadius.circular(7)),
+                  borderRadius: BorderRadius.circular(7),
+                ),
               ),
               SizedBox(
                 width: 400,

lib/country_code_picker.dart

@@ -79,7 +79,7 @@ class CountryCodePicker extends StatefulWidget {
   final bool showDropDownButton;
 
   /// [BoxDecoration] for the flag image
-  final Decoration flagDecoration;
+  final Decoration? flagDecoration;
 
   CountryCodePicker({
     this.onChanged,
@@ -302,6 +302,7 @@ class CountryCodePickerState extends State<CountryCodePicker> {
                 barrierColor: widget.barrierColor,
                 hideSearch: widget.hideSearch,
                 closeIcon: widget.closeIcon,
+                flagDecoration: widget.flagDecoration,
               ),
             ),
           ),

lib/selection_dialog.dart

@@ -44,8 +44,7 @@ class SelectionDialog extends StatefulWidget {
     this.barrierColor,
     this.hideSearch = false,
     this.closeIcon,
-  })  : assert(searchDecoration != null, 'searchDecoration must not be null!'),
+  })  : this.searchDecoration = searchDecoration.prefixIcon == null
-        this.searchDecoration = searchDecoration.prefixIcon == null
             ? searchDecoration.copyWith(prefixIcon: Icon(Icons.search))
             : searchDecoration,
         super(key: key);