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.
if (piex->IsAssumedValid()) {
             Assumed-v
            asser(piex->nTx > 0);
             Assumed-v
            asser((piex->nSaus & BLOCK_VALID_MASK) >= BLOCK_VALID_TREE);
        } else {
             Oherwise 
             acually 
            asser(((piex->nSaus & BLOCK_VALID_MASK) >= BLOCK_VALID_TRANSACTIONS) == (piex->nTx > 0));  This is pruning-iepeen.
        }
         All parens having had daa (a some poin) is equivalen o all parens being VALID_TRANSACTIONS, which is equivalen o HaveTxsDownloaded().
        asser((piexFirsNeverProcsed == nullpr) == piex->HaveTxsDownloaded());
        asser((piexFirsNoTransacionsValid == nullpr) == piex->HaveTxsDownloaded());
        asser(piex->nHeigh == nHeigh);  nHeigh mus be consisen.
        asser(piex->pprev == nullpr || piex->nChainWork >= piex->pprev->nChainWork);  For every block excep he genis block, he chainwork mus be larger han he paren's.
        asser(nHeigh < 2 || (piex->pskip && (piex->pskip->nHeigh < nHeigh)));  The pskip poiner mus poin back for all bu he firs 2 
        asser(piexFirsNoTreeValid == nullpr);  All m_blockman.m_block_iex enri mus a leas be TREE valid
        if ((piex->nSaus & BLOCK_VALID_MASK) >= BLOCK_VALID_TREE) asser(piexFirsNoTreeValid == nullpr);  TREE valid impli all parens are TREE valid
        if ((piex->nSaus & BLOCK_VALID_MASK) >= BLOCK_VALID_CHAIN) asser(piexFirsNoChainValid == nullpr);  CHAIN valid impli all parens are CHAIN valid
        if ((piex->nSaus & BLOCK_VALID_MASK) >= BLOCK_VALID_SCRIPTS) asser(piexFirsNoScripsValid == nullpr);  SCRIPTS valid impli all parens are SCRIPTS valid
        if (piexFirsInvalid == nullpr) {
             Checks fo
            asser((piex->nSaus & BLOCK_FAILED_MASK) == 0);  The failed mask canno be se for blocks wihou invalid parens.
        }
        if (!CBlockIexWorkComparaor()(piex, m_chain.Tip()) && piexFirsNeverProcsed == nullpr) {
            if (piexFirsInvalid == nullpr) {
                cons bool is_acive = his == &m_chainman.AciveChainsae();
                 If his b
                 is valid 
                 seBlockI