Passe YearAdapter an DiffUtil an

app/src/main/java/com/cyb3rko/techniklogger/recycler/YearAdapter.kt

@@ -23,7 +23,7 @@ class YearAdapter(
     }
 
     override fun onBindViewHolder(holder: ViewHolder, position: Int) {
-        val entry = getItem(position)
+        val entry = currentList[position]
         val name = entry.getString("name")!!
         holder.nameView.text = name
         holder.cardView.setOnClickListener {
@@ -31,6 +31,8 @@ class YearAdapter(
         }
     }
 
+    override fun getItemCount() = currentList.size
+
     class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
         val cardView: CardView = view.findViewById(R.id.root)
         val nameView: TextView = view.findViewById(R.id.name_text)