diff --git a/CHANGELOG.md b/CHANGELOG.md
index 535d428..40ea259 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,10 +1,16 @@
+## v4.2.11 (Apr 18, 2024)
+
+### Improvements
+- Fixed the bug that there are duplicate channels in `GroupChannelCollection`
+- Added default mimeType in `FileMessageCreateParams`
+
 ## v4.2.10 (Apr 9, 2024)
 
 ### Features
 - Added the privacy manifest file for iOS
 
 ### Improvements
-- Fixed the bug that there are duplicated channels in `GroupChannelCollection`
+- Fixed the bug that there are duplicate channels in `GroupChannelCollection`
 
 ## v4.2.9 (Apr 3, 2024)
 
diff --git a/README.md b/README.md
index 12da381..4929164 100644
--- a/README.md
+++ b/README.md
@@ -50,7 +50,7 @@ Before installing Sendbird Chat SDK, you need to create a Sendbird application o
 
 ```yaml
 dependencies:
-  sendbird_chat_sdk: ^4.2.10
+  sendbird_chat_sdk: ^4.2.11
 ```
 
 - Run `flutter pub get` command in your project directory.
diff --git a/lib/src/internal/main/chat/chat.dart b/lib/src/internal/main/chat/chat.dart
index cac13a5..6e28be6 100644
--- a/lib/src/internal/main/chat/chat.dart
+++ b/lib/src/internal/main/chat/chat.dart
@@ -60,7 +60,7 @@ part 'chat_notifications.dart';
 part 'chat_push.dart';
 part 'chat_user.dart';
 
-const sdkVersion = '4.2.10';
+const sdkVersion = '4.2.11';
 
 // Internal implementation for main class. Do not directly access this class.
 class Chat with WidgetsBindingObserver {
diff --git a/lib/src/internal/main/chat_manager/collection_manager/group_channel_collection_manager.dart b/lib/src/internal/main/chat_manager/collection_manager/group_channel_collection_manager.dart
index 0f7f073..b935088 100644
--- a/lib/src/internal/main/chat_manager/collection_manager/group_channel_collection_manager.dart
+++ b/lib/src/internal/main/chat_manager/collection_manager/group_channel_collection_manager.dart
@@ -170,15 +170,7 @@ extension GroupChannelCollectionManager on CollectionManager {
 
     if (addedChannels != null && addedChannels.isNotEmpty) {
       for (final addedChannel in addedChannels) {
-        bool isChannelExists = false;
-        for (final channel in channelCollection.channelList) {
-          if (channel.channelUrl == addedChannel.channelUrl) {
-            isChannelExists = true;
-            break;
-          }
-        }
-
-        if (!isChannelExists) {
+        if (!_isChannelExists(channelCollection, addedChannel.channelUrl)) {
           if (await channelCollection.canAddChannel(
               eventSource, addedChannel)) {
             addedChannelsForEvent.add(addedChannel);
@@ -187,7 +179,7 @@ extension GroupChannelCollectionManager on CollectionManager {
       }
 
       if (addedChannelsForEvent.isNotEmpty) {
-        channelCollection.channelList.addAll(addedChannelsForEvent);
+        _addChannel(channelCollection, addedChannelsForEvent);
       }
     }
 
@@ -220,15 +212,7 @@ extension GroupChannelCollectionManager on CollectionManager {
 
         if (eventSource == CollectionEventSource.channelChangeLogs &&
             !isUpdatedChannelInChannelList) {
-          bool isChannelExists = false;
-          for (final channel in channelCollection.channelList) {
-            if (channel.channelUrl == updatedChannel.channelUrl) {
-              isChannelExists = true;
-              break;
-            }
-          }
-
-          if (!isChannelExists) {
+          if (!_isChannelExists(channelCollection, updatedChannel.channelUrl)) {
             if (await channelCollection.canAddChannel(
                 eventSource, updatedChannel)) {
               addedChannelsForEvent.add(updatedChannel);
@@ -238,7 +222,7 @@ extension GroupChannelCollectionManager on CollectionManager {
       }
 
       if (addedChannelsForEvent.isNotEmpty) {
-        channelCollection.channelList.addAll(addedChannelsForEvent);
+        _addChannel(channelCollection, addedChannelsForEvent);
       }
     }
 
@@ -282,4 +266,36 @@ extension GroupChannelCollectionManager on CollectionManager {
       }
     }
   }
+
+  bool _isChannelExists(GroupChannelCollection collection, String channelUrl) {
+    for (final channel in collection.channelList) {
+      if (channel.channelUrl == channelUrl) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  void _addChannel(
+    GroupChannelCollection channelCollection,
+    List<GroupChannel> addedChannels,
+  ) {
+    final channelList = channelCollection.channelList;
+    for (final addedChannel in addedChannels) {
+      bool isUpdated = false;
+
+      for (int index = 0; index < channelList.length; index++) {
+        final channel = channelList[index];
+        if (addedChannel.channelUrl == channel.channelUrl) {
+          channelList[index] = addedChannel;
+          isUpdated = true;
+          break;
+        }
+      }
+
+      if (isUpdated == false) {
+        channelList.add(addedChannel);
+      }
+    }
+  }
 }
diff --git a/lib/src/public/main/collection/group_channel_collection/group_channel_collection.dart b/lib/src/public/main/collection/group_channel_collection/group_channel_collection.dart
index f94ed6e..d53bf13 100644
--- a/lib/src/public/main/collection/group_channel_collection/group_channel_collection.dart
+++ b/lib/src/public/main/collection/group_channel_collection/group_channel_collection.dart
@@ -239,15 +239,15 @@ class GroupChannelCollection {
     GroupChannel addedChannel, {
     bool checkToUpdateChannel = false,
   }) async {
+    if (_isLoadedOnce == false) {
+      return false;
+    }
+
     if (eventSource == CollectionEventSource.channelCacheLoadMore ||
         eventSource == CollectionEventSource.channelLoadMore) {
       return true;
     }
 
-    if (_isLoadedOnce == false) {
-      return false;
-    }
-
     if (channelList.isNotEmpty && hasMore) {
       final a = channelList.last;
       final b = addedChannel;
diff --git a/lib/src/public/main/params/message/file_message_create_params.dart b/lib/src/public/main/params/message/file_message_create_params.dart
index 9fe4868..dd28a2d 100644
--- a/lib/src/public/main/params/message/file_message_create_params.dart
+++ b/lib/src/public/main/params/message/file_message_create_params.dart
@@ -63,13 +63,13 @@ class FileMessageCreateParams extends BaseMessageCreateParams {
           break;
       }
     } else {
-      fileMimeType = lookupMimeType(file.path)!;
+      fileMimeType = lookupMimeType(file.path);
     }
 
     fileInfo = FileInfo.fromFile(
       fileName: fileName ?? 'file',
       file: file,
-      mimeType: fileMimeType,
+      mimeType: fileMimeType ?? 'application/octet-stream',
     );
   }
 
@@ -99,7 +99,8 @@ class FileMessageCreateParams extends BaseMessageCreateParams {
           pushNotificationDeliveryOption: pushNotificationDeliveryOption,
           isPinnedMessage: isPinnedMessage,
         ) {
-    String? fileMimeType = lookupMimeType('', headerBytes: fileBytes);
+    final fileMimeType = lookupMimeType('', headerBytes: fileBytes);
+
     if (fileMimeType != null) {
       mimeType = fileMimeType;
     } else if (mimeType == null) {
@@ -109,7 +110,7 @@ class FileMessageCreateParams extends BaseMessageCreateParams {
     fileInfo = FileInfo.fromFileBytes(
       fileBytes: fileBytes,
       fileName: fileName ?? 'file',
-      mimeType: mimeType,
+      mimeType: mimeType ?? 'application/octet-stream',
     );
   }
 
@@ -130,8 +131,8 @@ class FileMessageCreateParams extends BaseMessageCreateParams {
         PushNotificationDeliveryOption.normal,
     bool isPinnedMessage = false,
   })  : fileInfo = FileInfo.fromFileUrl(
-          fileName: fileName ?? 'image',
-          mimeType: mimeType ?? 'image/jpeg',
+          fileName: fileName ?? 'file',
+          mimeType: mimeType ?? 'application/octet-stream',
           fileUrl: fileUrl,
           fileSize: fileSize,
         ),
diff --git a/pubspec.yaml b/pubspec.yaml
index 8b07108..d07871b 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,6 @@
 name: sendbird_chat_sdk
 description: With Sendbird Chat for Flutter, you can easily build an in-app chat with all the essential messaging features.
-version: 4.2.10
+version: 4.2.11
 homepage: https://sendbird.com
 repository: https://github.com/sendbird/sendbird-chat-sdk-flutter
 documentation: https://sendbird.com/docs/chat/sdk/v4/flutter/getting-started/send-first-message