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.
*
     * May not be called in a validationinterface callback.
     *
     * @param[in]   block The block we want to process.
     * @param[in]   force_processing Process this block even if unrequested; used for non-network block sources.
     * @param[in]   min_pow_checked  True if proof-of-work anti-DoS checks have
     *                               been done by caller for headers chain
     *                               (note: only affects headers acceptance; if
     *                               block header is already present in block
     *                               index then this parameter has no effect)
     * @param[out]  new_block A boolean which is set to indicate if the block was first received via this call
     * @returns     If the block was processed, independently of block validity
     */
    bool ProcessNewBlock(const std::shared_ptr<const CBlock>& block, bool force_processing, bool min_pow_checked, bool* new_block) LOCKS_EXCLUDED(cs_main);
    /**
     * Process incoming block headers.
     *
     * May not be called in a
     * validationinterface callback.
     *
     * @param[in]  block The block headers themselves
     * @param[in]  min_pow_checked  True if proof-of-work anti-DoS checks have been done by caller for headers chain
     * @param[out] state This may be set to an Error state if any error occurred processing them
     * @param[out] ppindex If set, the pointer will be set to point to the last new block index object for the given headers
     */
    bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& block, bool min_pow_checked, BlockValidationState& state, const CBlockIndex** ppindex = nullptr) LOCKS_EXCLUDED(cs_main);
    /**
     * Try to add a transaction to the memory pool.
     *
     * @param[in]  tx              The transaction to submit for mempool acceptance.