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 
outputs[key.n] = std::move(coin);
        } else {
            return error("%s: unable to read value", __func__);
        }
        pcursor->Next();
    }
    if (!outputs.empty()) {
        ApplyStats(stats, ss, prevkey, outputs);
    }
    stats.hashSerialized = ss.GetHash();
    stats.nDiskSize = view->EstimateSize();
    return true;
}
static UniValue pruneblockchain(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() != 1)
        throw std::runtime_error(
            RPCHelpMan{"pruneblockchain", "",
                {
                    {"height", RPCArg::Type::NUM, RPCArg::Optional::NO, "The block height to prune up to. May be set to a discrete height, or a unix timestamp\n"
            "                  to prune blocks whose block time is at least 2 hours older than the provided timestamp."},
                },
                RPCResult{
            "n    (numeric) Height of the last block pruned.\n"
                },
                RPCExamples{
                    HelpExampleCli("pruneblockchain", "1000")
            + HelpExampleRpc("pruneblockchain", "1000")
                },
            }.ToString());