fix bug

android/src/main/java/io/openim/flutter_openim_sdk/util/JsonUtil.java

@@ -4,6 +4,13 @@ import org.json.JSONObject;
 
 public class JsonUtil {
     public static String toString(Object o) {
+        if (o instanceof String) {
+            StringBuffer buffer = new StringBuffer();
+            buffer.append("\"");
+            buffer.append(o);
+            buffer.append("\"");
+            return buffer.toString();
+        }
         Object obj = JSONObject.wrap(o);
         if (null != obj) {
             return obj.toString();

lib/src/manager/im_group_manager.dart

@@ -126,7 +126,7 @@ class GroupManager {
     return _channel
         .invokeMethod('getGroupsInfo', _buildParam({'gidList': gidList}))
         .then((value) {
-      List list = _formatJson(value) ?? [];
+      List list = _formatJson(value);
       return list.map((e) => GroupInfo.fromJson(e)).toList();
     });
   }