code: @Nullable
      ViewHolder popRecycledViewHolder(int itemType) {
          Deque<ViewHolder> deque = mViewHolders.get(itemType);
          return deque == null || deque.isEmpty() ? null : deque.pop();
      }
docs: Returns, if exists, a view of the type <code>typeView</code>.
  
  @param itemType the type of view that you want.
  @return a viewHolder of the type <code>typeView</code>. <code>null</code> if
  not found.