code: public boolean isContentTheSame(@Nullable final T oldItem, @Nullable final T newItem) {
          return (oldItem == newItem) || (oldItem != null && oldItem.equals(newItem));
      }
docs: Called by the DiffUtil when it wants to check whether two items have the same data.
  DiffUtil uses this information to detect if the contents of an item has changed.
  <p>
  DiffUtil uses this method to check equality instead of {@link Object#equals(Object)}
  so that you can change its behavior depending on your UI.
  For example, if you are using DiffUtil with a
  {@link android.support.v7.widget.RecyclerView.Adapter RecyclerView.Adapter}, you should
  return whether the items' visual representations are the same.
  <p>
  This method is called only if {@link #isItemTheSame(Object, Object)} returns
  {@code true} for these items.
  
  @param oldItem The position of the item in the old list
  @param newItem The position of the item in the new list which replaces the
  oldItem
  @return True if the contents of the items are the same or false if they are different.