fix linter

lib/src/message_input.dart

@@ -324,6 +324,8 @@ class _MessageInputState extends State<MessageInput> {
       ),
     );
 
+    attachment.url = res.file;
+
     setState(() {
       attachment.uploaded = true;
     });
@@ -404,9 +406,9 @@ class _MessageInputState extends State<MessageInput> {
 }
 
 class _SendingAttachment {
-  final String url;
   final File file;
   final FileType type;
+  String url;
   bool uploaded = false;
 
   _SendingAttachment({

lib/src/message_widget.dart

@@ -508,8 +508,9 @@ class _MessageWidgetState extends State<MessageWidget>
                             return Text(
                               reactionToEmoji[reactionType] ?? '?',
                             ) as Widget; //TODO refactor
-                  }).toList()
+                          }).toList() +
-                        ..add(Padding(
+                          [
+                            Padding(
                               padding: const EdgeInsets.only(left: 4.0),
                               child: Text(
                                 widget.message.reactionCounts.values
@@ -517,7 +518,8 @@ class _MessageWidgetState extends State<MessageWidget>
                                     .toString(),
                                 style: TextStyle(color: Colors.white),
                               ),
-                        )))
+                            )
+                          ])
               : SizedBox(),
         ),
       ),

lib/src/thread_header.dart

@@ -2,8 +2,6 @@ import 'package:flutter/material.dart';
 import 'package:stream_chat/stream_chat.dart';
 import 'package:stream_chat_flutter/src/stream_chat_theme.dart';
 
-import 'stream_channel.dart';
-
 class ThreadHeader extends StatelessWidget implements PreferredSizeWidget {
   final bool showBackButton;
   final VoidCallback onBackPressed;
@@ -19,7 +17,6 @@ class ThreadHeader extends StatelessWidget implements PreferredSizeWidget {
 
   @override
   Widget build(BuildContext context) {
-    final channel = StreamChannel.of(context).channel;
     return AppBar(
       automaticallyImplyLeading: false,
       elevation: 1,