fix #6: ChannelListView NULL error when a channel has no messages

lib/src/channel_list_view.dart

@@ -126,7 +126,7 @@ class _ChannelListViewState extends State<ChannelListView> {
                 return widget.errorBuilder(snapshot.error);
               }
 
-              String message = snapshot.error.toString();
+              var message = snapshot.error.toString();
               if (snapshot.error is DioError) {
                 final dioError = snapshot.error as DioError;
                 if (dioError.type == DioErrorType.RESPONSE) {

lib/src/channel_preview.dart

@@ -68,6 +68,9 @@ class ChannelPreview extends StatelessWidget {
       stream: channel.lastMessageAtStream,
       initialData: channel.lastMessageAt,
       builder: (context, snapshot) {
+        if (!snapshot.hasData) {
+          return SizedBox();
+        }
         final lastMessageAt = snapshot.data.toLocal();
 
         String stringDate;

lib/src/message_widget.dart

@@ -93,7 +93,7 @@ class _MessageWidgetState extends State<MessageWidget>
     final alignment =
         _isMyMessage ? Alignment.centerRight : Alignment.centerLeft;
 
-    List<Widget> row = <Widget>[
+    var row = <Widget>[
       Column(
         crossAxisAlignment:
             _isMyMessage ? CrossAxisAlignment.end : CrossAxisAlignment.start,
@@ -302,7 +302,7 @@ class _MessageWidgetState extends State<MessageWidget>
     }));
 
     if (widget.message.text.trim().isNotEmpty) {
-      String text = widget.message.text;
+      var text = widget.message.text;
       text = _replaceMentions(text);
 
       column.addAll(