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 
const CTxMemPoolEntry &e = *it;
    UniValue info(UniValue::VOBJ);
    entryToJSON(::mempool, info, e);
    return info;
}
static UniValue getblockhash(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() != 1)
        throw std::runtime_error(
            RPCHelpMan{"getblockhash",
                "\nReturns hash of block in best-block-chain at height provided.\n",
                {
                    {"height", RPCArg::Type::NUM, RPCArg::Optional::NO, "The height index"},
                },
                RPCResult{
            "\"hash\"         (string) The block hash\n"
                },
                RPCExamples{
                    HelpExampleCli("getblockhash", "1000")
            + HelpExampleRpc("getblockhash", "1000")
                },
            }.ToString());
    LOCK(cs_main);
    int nHeight = request.params[0].get_int();
    if (nHeight < 0 || nHeight > chainActive.Height())
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Block height out of range");
    CBlockIndex* pblockindex = chainActive[nHeight];
    return pblockindex->GetBlockHash().GetHex();
}
static UniValue getblockheader(const JSONRPCRequest& request)