  "mempoolminfee": 0.00000000

When the minrelaytxfee is > 0.

{
    if (request.fHelp || request.params.size() != 0) {
        throw std::runtime_error(
            "savemempool\n"
            "\nDumps the mempool to disk.\n"
            "\nExamples:\n"
            + HelpExampleCli("savemempool", "")
            + HelpExampleRpc("savemempool", "")
        );
    }
    if (!DumpMempool()) {
        throw JSONRPCError(RPC_MISC_ERROR, "Unable to dump mempool to disk");
    }
    return NullUniValue;
}
static const CRPCCommand commands[] =
{ 
  
    { "blockchain",         "getblockchaininfo",      &getblockchaininfo,      {} },
    { "blockchain",         "getchaintxstats",        &getchaintxstats,        {"nblocks", "blockhash"} },
    { "blockchain",         "getbestblockhash",       &getbestblockhash,       {} },