fix nullability issues and crash in sample app, added title to main screen

Author: luca

lib/src/main/java/com/kirkbushman/zammad/models/OnlineNotification.kt

@@ -19,10 +19,10 @@ data class OnlineNotification(
     val objId: Int,
 
     @Json(name = "object")
-    val objectType: String,
+    val objectType: String?,
 
     @Json(name = "type")
-    val type: NotificationType,
+    val type: NotificationType?,
 
     @Json(name = "seen")
     val seen: Boolean,

sampleapp/src/main/res/layout/activity_main.xml

@@ -1,9 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
-<androidx.coordinatorlayout.widget.CoordinatorLayout
-        xmlns:android="http://schemas.android.com/apk/res/android"
+<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:tools="http://schemas.android.com/tools"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
+        xmlns:app="http://schemas.android.com/apk/res-auto"
         tools:context=".MainActivity">
 
     <com.google.android.material.appbar.AppBarLayout
@@ -14,7 +14,8 @@
         <androidx.appcompat.widget.Toolbar
                 android:id="@+id/toolbar"
                 android:layout_width="match_parent"
-                android:layout_height="?attr/actionBarSize" />
+                android:layout_height="?attr/actionBarSize"
+                app:title="@string/app_name" />
 
     </com.google.android.material.appbar.AppBarLayout>
 

sampleapp/src/main/res/layout/item_overview.xml

@@ -1,8 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
-              android:orientation="vertical"
-              android:layout_width="match_parent"
-              android:layout_height="wrap_content">
+        android:id="@+id/container"
+        android:orientation="vertical"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content">
 
     <TextView
             android:id="@+id/overview_name"