diff_buf_delete(buf_T *buf)
{
    int		i;
    tabpage_T	*tp;

    FOR_ALL_TABPAGES(tp)
    {
	i = diff_buf_idx_tp(buf, tp);
	if (i != DB_COUNT)
	{
	    tp->tp_diffbuf[i] = NULL;
	    tp->tp_diff_invalid = TRUE;
	    if (tp == curtab)
	    {
		// don't redraw right away, more might change or buffer state
		// is invalid right now
		need_diff_redraw = TRUE;
		redraw_later(VALID);
	    }
	}
    }
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.