code: @MustBeLocked (ELockType.WRITE)
    @Nonnull
    protected final IMPLTYPE internalCreateItem (@Nonnull final IMPLTYPE aNewItem)
    {
      return internalCreateItem (aNewItem, true);
    }
docs: Add an item including invoking the callback. Must only be invoked inside a
  write-lock.
  
  @param aNewItem
  The item to be added. May not be <code>null</code>.
  @return The passed parameter as-is. Never <code>null</code>.
  @throws IllegalArgumentException
  If an item with the same ID is already contained