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 
result.pushKV("nonce", (uint64_t)block.nNonce);
    result.pushKV("bits", strprintf("%08x", block.nBits));
    result.pushKV("difficulty", GetDifficulty(blockindex));
    result.pushKV("chainwork", blockindex->nChainWork.GetHex());
    result.pushKV("nTx", (uint64_t)blockindex->nTx);
    if (blockindex->pprev)
        result.pushKV("previousblockhash", blockindex->pprev->GetBlockHash().GetHex());
    if (pnext)
        result.pushKV("nextblockhash", pnext->GetBlockHash().GetHex());
    return result;
}
static UniValue getblockcount(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() != 0)
        throw std::runtime_error(
            RPCHelpMan{"getblockcount",
                "\nReturns the number of blocks in the longest blockchain.\n",
                {},
                RPCResult{
            "n    (numeric) The current block count\n"
                },
                RPCExamples{
                    HelpExampleCli("getblockcount", "")
            + HelpExampleRpc("getblockcount", "")
                },
            }.ToString());
    LOCK(cs_main);
    return chainActive.Height();
}
static UniValue getbestblockhash(const JSONRPCRequest& request)