check if user.extradata["image"] is null

lib/src/message_text.dart

@@ -24,7 +24,11 @@ class MessageText extends StatelessWidget {
     final text = _replaceMentions(message.text);
     return MarkdownBody(
       data: text,
-      onTapLink: (link) {
+      onTapLink: (
+        String link,
+        String href,
+        String title,
+      ) {
         if (link.startsWith('@')) {
           final mentionedUser = message.mentionedUsers.firstWhere(
             (u) => '@${u.name.replaceAll(' ', '')}' == link,

lib/src/user_avatar.dart

@@ -38,7 +38,9 @@ class UserAvatar extends StatelessWidget {
           decoration: BoxDecoration(
             color: StreamChatTheme.of(context).accentColor,
           ),
-          child: user.extraData?.containsKey('image') ?? false
+          child: (user.extraData?.containsKey('image') == true &&
+                  user.extraData['image'] != null &&
+                  user.extraData['image'] != '')
               ? CachedNetworkImage(
                   imageUrl: user.extraData['image'],
                   errorWidget: (_, __, ___) {