Can change group description

lib/helpers/groups_helper.dart

@@ -257,7 +257,7 @@ class GroupsHelper {
         virtualDirectory: nullToEmpty(map["virtual_directory"]),
         following: map["following"],
         timeCreate: map["time_create"],
-        description: map["description"],
+        description: nullToEmpty(map["description"]),
         url: nullToEmpty(map["url"]),
         likes: map["number_likes"],
         userLike: map["is_liking"],

lib/models/advanced_group_info.dart

@@ -10,7 +10,7 @@ import 'group.dart';
 
 class AdvancedGroupInfo extends Group implements LikeElement {
   final int timeCreate;
-  final String description;
+  String description;
   String url;
   int likes;
   bool userLike;

lib/ui/screens/group_settings_screen.dart

@@ -121,7 +121,19 @@ class _GroupSettingsScreenState extends SafeState<GroupSettingsScreen> {
             _groupSettings.url = s;
             _updateSettings();
           },
-        )
+        ),
+
+        // Group description
+        TextEditSettingsTile(
+            title: tr("Group description (optional)"),
+            currValue: _groupSettings.description,
+            maxLines: 3,
+            maxLength: 255,
+            allowEmptyValues: true,
+            onChanged: (s) {
+              _groupSettings.description = s;
+              _updateSettings();
+            }),
       ],
     );
   }