  "mempoolminfee": 0.00000000

When the minrelaytxfee is > 0.

{
    if (request.fHelp || request.params.size() != 0)
        throw std::runtime_error(
            "getbestblockhash\n"
            "\nReturns the hash of the best (tip) block in the longest blockchain.\n"
            "\nResult:\n"
            "\"hex\"      (string) the block hash hex encoded\n"
            "\nExamples:\n"
            + HelpExampleCli("getbestblockhash", "")
            + HelpExampleRpc("getbestblockhash", "")
        );
    LOCK(cs_main);
    return chainActive.Tip()->GetBlockHash().GetHex();
}
void RPCNotifyBlockChange(bool ibd, const CBlockIndex * pindex)
{
    if(pindex) {
        std::lock_guard<std::mutex> lock(cs_blockchange);
        latestblock.hash = pindex->GetBlockHash();
        latestblock.height = pindex->nHeight;
    }
    cond_blockchange.notify_all();
}
UniValue waitfornewblock(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() > 1)
        throw std::runtime_error(
            "waitfornewblock (timeout)\n"
            "\nWaits for a specific new block and returns useful info about it.\n"
            "\nReturns the current block on timeout or exit.\n"