Reported here: https://github.com/bitcoin/bitcoin/pull/10244#issuecomment-378035305

Travis log here: https://travis-ci.org/bitcoin/bitcoin/jobs/361243719#L2810

Note the JSON exception:

```
test_framework.authproxy.JSONRPCException: The mempool was not loaded yet (-1) 
```

That exception was introduced here: https://github.com/bitcoin/bitcoin/commit/cb1e319fe9e198c9c5cf5236fe9af5a3d748b9e8#diff-a0c8f511d90e83aa9b5857e819ced344R1617

cc @jtimon 
"  \"maxfee\": xxxxx,          (numeric) Maximum fee in the block\n"
            "  \"maxfeerate\": xxxxx,      (numeric) Maximum feerate (in satoshis per virtual byte)\n"
            "  \"maxtxsize\": xxxxx,       (numeric) Maximum transaction size\n"
            "  \"medianfee\": xxxxx,       (numeric) Truncated median fee in the block\n"
            "  \"mediantime\": xxxxx,      (numeric) The block median time past\n"
            "  \"mediantxsize\": xxxxx,    (numeric) Truncated median transaction size\n"
            "  \"minfee\": xxxxx,          (numeric) Minimum fee in the block\n"
            "  \"minfeerate\": xxxxx,      (numeric) Minimum feerate (in satoshis per virtual byte)\n"
            "  \"mintxsize\": xxxxx,       (numeric) Minimum transaction size\n"
            "  \"outs\": xxxxx,            (numeric) The number of outputs\n"
            "  \"subsidy\": xxxxx,         (numeric) The block subsidy\n"
            "  \"swtotal_size\": xxxxx,    (numeric) Total size of all segwit transactions\n"
            "  \"swtotal_weight\": xxxxx,  (numeric) Total weight of all segwit transactions divided by segwit scale factor (4)\n"
            "  \"swtxs\": xxxxx,           (numeric) The number of segwit transactions\n"
            "  \"time\": xxxxx,            (numeric) The block time\n"
            "  \"total_out\": xxxxx,       (numeric) Total amount in all outputs (excluding coinbase and thus reward [ie subsidy + totalfee])\n"
            "  \"total_size\": xxxxx,      (numeric) Total size of all non-coinbase transactions\n"
            "  \"total_weight\": xxxxx,    (numeric) Total weight of all non-coinbase transactions divided by segwit scale factor (4)\n"
            "  \"totalfee\": xxxxx,        (numeric) The fee total\n"
            "  \"txs\": xxxxx,             (numeric) The number of transactions (excluding coinbase)\n"
            "  \"utxo_increase\": xxxxx,   (numeric) The increase/decrease in the number of unspent outputs\n"
            "  \"utxo_size_inc\": xxxxx,   (numeric) The increase/decrease in size for the utxo index (not discounting op_return and similar)\n"
            "}\n"
                },
                RPCExamples{
                    HelpExampleCli("getblockstats", "1000 '[\"minfeerate\",\"avgfeerate\"]'")
            + HelpExampleRpc("getblockstats", "1000 '[\"minfeerate\",\"avgfeerate\"]'")
                },
    };
    if (request.fHelp || !help.IsValidNumArgs(request.params.size())) {