static void free_duplicate_context(MpegEncContext *s)
{
    if (!s)
        return;

    av_freep(&s->sc.edge_emu_buffer);
    av_freep(&s->me.scratchpad);
    s->me.temp =
    s->sc.rd_scratchpad =
    s->sc.b_scratchpad =
    s->sc.obmc_scratchpad = NULL;

    av_freep(&s->dct_error_sum);
    av_freep(&s->me.map);
    av_freep(&s->me.score_map);
    av_freep(&s->blocks);
    av_freep(&s->block32);
    av_freep(&s->ac_val_base);
    s->block = NULL;
}

The product dereferences a pointer that it expects to be valid but is NULL.