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.
int ActiveHeight() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex()) { return ActiveChain().Height(); }
    CBlockIndex* ActiveTip() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex()) { return ActiveChain().Tip(); }
    node::BlockMap& BlockIndex() EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
    {
        AssertLockHeld(::cs_main);
        return m_blockman.m_block_index;
    }
    /**
     * Track versionbit status
     */
    mutable VersionBitsCache m_versionbitscache;
    
    
    bool IsSnapshotActive() const;
    std::optional<uint256> SnapshotBlockhash() const;
    
    bool IsSnapshotValidated() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main) { return m_snapshot_validated; }
    /**
     * Process an incoming block. This only returns after the best known valid
     * block is made active. Note that it does not, however, guarantee that the
     * specific block passed to it has been checked for validity!
     *
     * If you want to *possibly* get feedback on whether block is valid, you must
     * install a CValidationInterface (see validationinterface.h) - this will have
     * its BlockChecked method called whenever *any* block completes validation.
     *
     * Note that we guarantee that either the proof-of-work is valid on block, or
     * (and possibly also) BlockChecked will have been called.