prevent crash in NotificationsAdapter when avatar url is not set

app/src/main/java/com/keylesspalace/tusky/adapter/NotificationsAdapter.java

@@ -264,6 +264,9 @@ public class NotificationsAdapter extends RecyclerView.Adapter {
 
             displayNameView.setText(displayName);
 
+            if (TextUtils.isEmpty(avatarUrl)) {
+                avatar.setImageResource(R.drawable.avatar_default);
+            } else {
                 Picasso.with(context)
                         .load(avatarUrl)
                         .fit()
@@ -271,6 +274,7 @@ public class NotificationsAdapter extends RecyclerView.Adapter {
                         .placeholder(R.drawable.avatar_default)
                         .into(avatar);
             }
+        }
 
         void setupButtons(final NotificationActionListener listener, final String accountId) {
             avatar.setOnClickListener(v -> listener.onViewAccount(accountId));
@@ -407,7 +411,7 @@ public class NotificationsAdapter extends RecyclerView.Adapter {
         void setAvatars(@Nullable String statusAvatarUrl, @Nullable String notificationAvatarUrl) {
             Context context = statusAvatar.getContext();
 
-            if (statusAvatarUrl == null || statusAvatarUrl.isEmpty()) {
+            if (TextUtils.isEmpty(statusAvatarUrl)) {
                 statusAvatar.setImageResource(R.drawable.avatar_default);
             } else {
                 Picasso.with(context)
@@ -417,7 +421,7 @@ public class NotificationsAdapter extends RecyclerView.Adapter {
                         .into(statusAvatar);
             }
 
-            if (notificationAvatarUrl == null || notificationAvatarUrl.isEmpty()) {
+            if (TextUtils.isEmpty(notificationAvatarUrl)) {
                 notificationAvatar.setImageResource(R.drawable.avatar_default);
             } else {
                 Picasso.with(context)