  "mempoolminfee": 0.00000000

When the minrelaytxfee is > 0.

{
    UniValue result(UniValue::VOBJ);
    result.push_back(Pair("hash", blockindex->GetBlockHash().GetHex()));
    int confirmations = -1;
    
    if (chainActive.Contains(blockindex))
        confirmations = chainActive.Height() - blockindex->nHeight + 1;
    result.push_back(Pair("confirmations", confirmations));
    result.push_back(Pair("strippedsize", (int)::GetSerializeSize(block, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS)));
    result.push_back(Pair("size", (int)::GetSerializeSize(block, SER_NETWORK, PROTOCOL_VERSION)));
    result.push_back(Pair("weight", (int)::GetBlockWeight(block)));
    result.push_back(Pair("height", blockindex->nHeight));
    result.push_back(Pair("version", block.nVersion));
    result.push_back(Pair("versionHex", strprintf("%08x", block.nVersion)));
    result.push_back(Pair("merkleroot", block.hashMerkleRoot.GetHex()));
    UniValue txs(UniValue::VARR);
    for(const auto& tx : block.vtx)
    {
        if(txDetails)
        {
            UniValue objTx(UniValue::VOBJ);
            TxToUniv(*tx, uint256(), objTx, true, RPCSerializationFlags());
            txs.push_back(objTx);
        }
        else
            txs.push_back(tx->GetHash().GetHex());
    }