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.
* or stale blocks exist). It maps from parent-hash to child-disk-position.
     *
     * This function can also be used to read blocks from user-specified block files using the
     * -loadblock= option. There's no unknown-parent tracking, so the last two arguments are omitted.
     *
     *
     * @param[in]     fileIn                        FILE handle to file containing blocks to read
     * @param[in]     dbp                           (optional) Disk block position (only for reindex)
     * @param[in,out] blocks_with_unknown_parent    (optional) Map of disk positions for blocks with
     *                                              unknown parent, key is parent block hash
     *                                              (only used for reindex)
     * */
    void LoadExternalBlockFile(
        FILE* fileIn,
        FlatFilePos* dbp = nullptr,
        std::multimap<uint256, FlatFilePos>* blocks_with_unknown_parent = nullptr)
        EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex);
    /**
     * Update the on-disk chain state.
     * The caches and indexes are flushed depending on the mode we're called with
     * if they're too large, if it's been a while since the last write,
     * or always and in all cases if we're in prune mode and are deleting files.
     *
     * If FlushStateMode::NONE is used, then FlushStateToDisk(...) won't do anything
     * besides checking if we need to prune.
     *
     * @returns true unless a system error occurred
     */
    bool FlushStateToDisk(
        BlockValidationState& state,