the command "bitcoin-cli getblockstats 0000000000000000000c61ff8f761ce509fc8901d3c22d61fec89637042ea2ba" does not work.

It displays "error: Error parsing JSON:0000000000000000000c61ff8f761ce509fc8901d3c22d61fec89637042ea2ba"

but it should display the block stats like the documentation says.

also bitcoin-cli getblockstats 0 does not work. block number must be at least 1 to work. But blocks start at 0.

tested with 0.20.1 on freebsd, another user on IRC acknowledged the problem.
{
    
    
    batch.Write(DB_MUHASH, m_muhash);
    return true;
}
bool CoinStatsIndex::ReverseBlock(const CBlock& block, const CBlockIndex* pindex)
{
    CBlockUndo block_undo;
    std::pair<uint256, DBVal> read_out;
    const CAmount block_subsidy{GetBlockSubsidy(pindex->nHeight, Params().GetConsensus())};
    m_total_subsidy -= block_subsidy;
    
    if (pindex->nHeight > 0) {
        if (!UndoReadFromDisk(block_undo, pindex)) {
            return false;
        }
        if (!m_db->Read(DBHeightKey(pindex->nHeight - 1), read_out)) {
            return false;
        }
        uint256 expected_block_hash{pindex->pprev->GetBlockHash()};
        if (read_out.first != expected_block_hash) {
            LogPrintf("WARNING: previous block header belongs to unexpected block %s; expected %s\n",
                      read_out.first.ToString(), expected_block_hash.ToString());
            if (!m_db->Read(DBHashKey(expected_block_hash), read_out)) {
                return error("%s: previous block header not found; expected %s",
                             __func__, expected_block_hash.ToString());
            }
        }