Variable absoluteUrl can be null (this avoid app crashing)

app/src/main/java/chat/rocket/android/helper/Avatar.kt

@@ -4,13 +4,17 @@ import chat.rocket.android.widget.AbsoluteUrl
 import chat.rocket.android.widget.RocketChatAvatar
 import java.net.URLEncoder
 
-class Avatar(val absoluteUrl: AbsoluteUrl, val username: String) {
+class Avatar(val absoluteUrl: AbsoluteUrl?, val username: String) {
 
     val imageUrl: String
         /** REMARK
          * This is often a SVG image (see Rocket.Chat:server/startup/avatar.js)
          */
         get() {
+            val avatarUrl = "/avatar/" + URLEncoder.encode(username, "UTF-8")
+            if (absoluteUrl == null) {
+                return avatarUrl
+            }
             return absoluteUrl.from("/avatar/" + URLEncoder.encode(username, "UTF-8"))
         }