add null check to message list view

packages/stream_chat_flutter/lib/src/message_list_view.dart

@@ -386,9 +386,7 @@ class _MessageListViewState extends State<MessageListView> {
             1 // parent message
         ;
 
-    return ColoredBox(
-      color: MessageListViewTheme.of(context).backgroundColor!,
-      child: Stack(
+    final child = Stack(
       alignment: Alignment.center,
       children: [
         ConnectionStatusBuilder(
@@ -560,8 +558,7 @@ class _MessageListViewState extends State<MessageListView> {
                           const Offstage();
                     }
 
-                      const bottomMessageIndex =
-                          2; // 1 -> loader // 0 -> footer
+                    const bottomMessageIndex = 2; // 1 -> loader // 0 -> footer
 
                     final message = messages[i - 2];
                     Widget messageWidget;
@@ -588,8 +585,18 @@ class _MessageListViewState extends State<MessageListView> {
         if (widget.showFloatingDateDivider)
           _buildFloatingDateDivider(itemCount),
       ],
-      ),
     );
+
+    final backgroundColor = MessageListViewTheme.of(context).backgroundColor;
+
+    if (backgroundColor != null) {
+      return ColoredBox(
+        color: backgroundColor,
+        child: child,
+      );
+    }
+
+    return child;
   }
 
   Widget _buildThreadSeparator() {