fix: video thumbnails on web null error

packages/stream_chat_flutter/lib/src/attachment/file_attachment.dart

@@ -195,7 +195,7 @@ class _FileTypeImage extends StatelessWidget {
         shape: _getDefaultShape(context),
         child: source.when(
           local: () => StreamVideoThumbnailImage(
-            video: attachment.file!.path!,
+            video: attachment.file!.path,
             placeholderBuilder: (_) => const Center(
               child: SizedBox(
                 width: 20,
@@ -205,7 +205,7 @@ class _FileTypeImage extends StatelessWidget {
             ),
           ),
           network: () => StreamVideoThumbnailImage(
-            video: attachment.assetUrl!,
+            video: attachment.assetUrl,
             placeholderBuilder: (_) => const Center(
               child: SizedBox(
                 width: 20,

packages/stream_chat_flutter/lib/src/attachment/video_attachment.dart

@@ -41,7 +41,7 @@ class StreamVideoAttachment extends StreamAttachmentWidget {
         return _buildVideoAttachment(
           context,
           StreamVideoThumbnailImage(
-            video: attachment.file!.path!,
+            video: attachment.file!.path,
             thumbUrl: attachment.thumbUrl,
             constraints: constraints,
           ),
@@ -54,7 +54,7 @@ class StreamVideoAttachment extends StreamAttachmentWidget {
         return _buildVideoAttachment(
           context,
           StreamVideoThumbnailImage(
-            video: attachment.assetUrl!,
+            video: attachment.assetUrl,
             thumbUrl: attachment.thumbUrl,
             constraints: constraints,
           ),

packages/stream_chat_flutter/lib/src/gallery/gallery_footer.dart

@@ -219,8 +219,8 @@ class _StreamGalleryFooterState extends State<StreamGalleryFooter> {
                           child: AspectRatio(
                             aspectRatio: 1,
                             child: StreamVideoThumbnailImage(
-                              video: (attachment.file?.path ??
-                                  attachment.assetUrl)!,
+                              video:
+                                  attachment.file?.path ?? attachment.assetUrl,
                             ),
                           ),
                         ),

packages/stream_chat_flutter/lib/src/message_input/quoted_message_widget.dart

@@ -276,7 +276,7 @@ class _ParseAttachments extends StatelessWidget {
       'video': (_, attachment) {
         return StreamVideoThumbnailImage(
           key: ValueKey(attachment.assetUrl),
-          video: attachment.file?.path ?? attachment.assetUrl!,
+          video: attachment.file?.path ?? attachment.assetUrl,
           constraints: BoxConstraints.loose(const Size(32, 32)),
           errorBuilder: (_, __) => AttachmentError(
             constraints: BoxConstraints.loose(const Size(32, 32)),

packages/stream_chat_flutter/lib/src/message_input/stream_message_input.dart

@@ -1194,7 +1194,7 @@ class StreamMessageInputState extends State<StreamMessageInput>
                   104,
                 ),
               ),
-              video: (attachment.file?.path ?? attachment.assetUrl)!,
+              video: attachment.file?.path ?? attachment.assetUrl,
             ),
             Positioned(
               left: 8,

packages/stream_chat_flutter/lib/src/video/video_service.dart

@@ -21,6 +21,9 @@ class _IVideoService {
   ///
   /// Thumbnails are not supported on Web at this time.
   ///
+  /// If no [video] path is supplied, or if a thumbnail cannot be generated,
+  /// returns [generatePlaceholderThumbnail]. A stock placeholder image.
+  ///
   /// For desktop, you can specify the position of the video to generate
   /// the thumbnail.
   ///
@@ -29,14 +32,14 @@ class _IVideoService {
   /// creates lower quality of the thumbnail image, but it gets ignored for
   /// PNG format.
   Future<Uint8List?> generateVideoThumbnail({
-    required String video,
+    String? video,
     ImageFormat imageFormat = ImageFormat.PNG,
     int maxHeight = 0,
     int maxWidth = 0,
     int timeMs = 0,
     int quality = 10,
   }) async {
-    if (kIsWeb) {
+    if (kIsWeb || video == null) {
       final placeholder = await generatePlaceholderThumbnail();
       return placeholder;
     }

packages/stream_chat_flutter/lib/src/video/video_thumbnail_image.dart

@@ -8,13 +8,23 @@ import 'package:stream_chat_flutter/stream_chat_flutter.dart';
 import 'package:video_thumbnail/video_thumbnail.dart';
 
 /// {@template streamVideoThumbnailImage}
-/// Displays a video thumbnail for video attachments in a message.
+/// Displays a video thumbnail for video attachments.
+///
+/// [thumbUrl] is used if provided.
+///
+/// Else [video] (path to local or remote video) is used to generate
+/// a thumbnail from the video asset.
+///
+/// WARNING! a local path does not work on web.
+///
+/// If both [thumbUrl] and [video] are null, or if a thumbnail can't be
+/// generated, a stock default image will be used.
 /// {@endtemplate}
 class StreamVideoThumbnailImage extends StatefulWidget {
   /// {@macro streamVideoThumbnailImage}
   const StreamVideoThumbnailImage({
     super.key,
-    required this.video,
+    this.video,
     this.thumbUrl,
     this.constraints,
     this.fit = BoxFit.cover,
@@ -24,7 +34,7 @@ class StreamVideoThumbnailImage extends StatefulWidget {
   });
 
   /// Video path or url
-  final String video;
+  final String? video;
 
   /// Video thumbnail url
   final String? thumbUrl;