Add userNotFoundImageView to handle cases where there is not an username (nullable username).

app/src/main/java/chat/rocket/android/layouthelper/chatroom/AbstractMessageViewHolder.java

@@ -13,6 +13,7 @@ import chat.rocket.core.SyncState;
 
 public abstract class AbstractMessageViewHolder extends ModelViewHolder<PairedMessage> {
   protected final RocketChatAvatar avatar;
+  protected final ImageView userNotFoundAvatarImageView;
   protected final ImageView errorImageView;
   protected final TextView username;
   protected final TextView subUsername;
@@ -29,6 +30,7 @@ public abstract class AbstractMessageViewHolder extends ModelViewHolder<PairedMe
   public AbstractMessageViewHolder(View itemView, AbsoluteUrl absoluteUrl, String hostname) {
     super(itemView);
     avatar = itemView.findViewById(R.id.user_avatar);
+    userNotFoundAvatarImageView = itemView.findViewById(R.id.userNotFoundAvatarImageView);
     errorImageView = itemView.findViewById(R.id.errorImageView);
     username = itemView.findViewById(R.id.username);
     subUsername = itemView.findViewById(R.id.sub_username);

app/src/main/java/chat/rocket/android/layouthelper/chatroom/MessageNormalViewHolder.java

@@ -29,7 +29,7 @@ public class MessageNormalViewHolder extends AbstractMessageViewHolder {
   @Override
   protected void bindMessage(PairedMessage pairedMessage, boolean autoloadImages) {
     MessageRenderer messageRenderer = new MessageRenderer(pairedMessage.target, autoloadImages);
-    messageRenderer.showAvatar(avatar, hostname);
+    messageRenderer.showAvatar(avatar, hostname, userNotFoundAvatarImageView);
     messageRenderer.showUsername(username, subUsername);
     messageRenderer.showTimestampOrMessageState(timestamp);
     messageRenderer.showBody(body);

app/src/main/java/chat/rocket/android/layouthelper/chatroom/MessageSystemViewHolder.java

@@ -24,7 +24,7 @@ public class MessageSystemViewHolder extends AbstractMessageViewHolder {
   @Override
   protected void bindMessage(PairedMessage pairedMessage, boolean autoloadImages) {
     MessageRenderer messageRenderer = new MessageRenderer(pairedMessage.target, autoloadImages);
-    messageRenderer.showAvatar(avatar, hostname);
+    messageRenderer.showAvatar(avatar, hostname, userNotFoundAvatarImageView);
     messageRenderer.showUsername(username, subUsername);
     messageRenderer.showTimestampOrMessageState(timestamp);
     if (pairedMessage.target != null) {

app/src/main/java/chat/rocket/android/renderer/MessageRenderer.kt

 package chat.rocket.android.renderer
 
 import android.view.View
+import android.widget.ImageView
 import android.widget.TextView
 import chat.rocket.android.R
 import chat.rocket.android.helper.DateTime
@@ -18,19 +19,20 @@ class MessageRenderer(val message: Message, val autoLoadImage: Boolean) {
     /**
      * Show user's avatar image in RocketChatAvatar widget.
      */
-    fun showAvatar(rocketChatAvatarWidget: RocketChatAvatar, hostname: String) {
+    fun showAvatar(rocketChatAvatarWidget: RocketChatAvatar, hostname: String, userNotFoundAvatarImageView: ImageView) {
         if (message.avatar != null) {
             // Load user's avatar image from Oauth provider URI.
             rocketChatAvatarWidget.loadImage(message.avatar)
         } else {
-            // Load user's avatar image from Rocket.Chat URI (only if username is not null).
             val username: String? = message.user?.username
+            // Load user's avatar image from Rocket.Chat URI if username is not null.
             if (username != null) {
                 rocketChatAvatarWidget.loadImage(RocketChatUserAvatar(hostname, username).imageUri)
+            } else {
+                // Hide RocketChatAvatar widget and show an "user not found" avatar.
+                rocketChatAvatarWidget.visibility = View.GONE
+                userNotFoundAvatarImageView.visibility = View.VISIBLE
             }
-            /**
-             * TODO Load default image for nullable username.
-             */
         }
     }
 

app/src/main/res/drawable/ic_user_not_found_avatar_black_24dp.xml

+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0">
+    <path
+        android:pathData="M-0,0L24,0L24,24L-0,24L-0,0ZM11.963,17.661L12.036,17.661L17.162,17.661C17.162,13.975 13.979,13.915 13.178,12.982L13.082,12.474C14.095,11.946 14.807,10.699 14.807,9.245C14.807,7.313 13.55,5.746 12,5.746C10.45,5.746 9.193,7.313 9.193,9.245C9.193,10.712 9.917,11.966 10.944,12.486L10.86,12.933C10.129,13.913 6.837,13.912 6.837,17.661L11.963,17.661Z"
+        android:fillColor="#FF000000"/>
+</vector>
\ No newline at end of file

app/src/main/res/layout/list_item_normal_message.xml

@@ -20,6 +20,14 @@
       android:layout_height="32dp"
       android:layout_margin="8dp" />
 
+    <ImageView
+      android:id="@+id/userNotFoundAvatarImageView"
+      android:layout_width="32dp"
+      android:layout_height="32dp"
+      android:layout_margin="8dp"
+      app:srcCompat="@drawable/ic_user_not_found_avatar_black_24dp"
+      android:visibility="gone" />
+
     <LinearLayout
       android:layout_width="match_parent"
       android:layout_height="wrap_content"

app/src/main/res/layout/list_item_system_message.xml

@@ -19,6 +19,14 @@
       android:layout_height="32dp"
       android:layout_margin="8dp" />
 
+    <ImageView
+      android:id="@+id/userNotFoundAvatarImageView"
+      android:layout_width="32dp"
+      android:layout_height="32dp"
+      android:layout_margin="8dp"
+      app:srcCompat="@drawable/ic_user_not_found_avatar_black_24dp"
+      android:visibility="gone" />
+
     <LinearLayout
       android:layout_width="match_parent"
       android:layout_height="wrap_content"