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 
throw std::runtime_error(help.ToString());
    }
    LOCK(cs_main);
    CBlockIndex* pindex;
    if (request.params[0].isNum()) {
        const int height = request.params[0].get_int();
        const int current_tip = chainActive.Height();
        if (height < 0) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Target block height %d is negative", height));
        }
        if (height > current_tip) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Target block height %d after current tip %d", height, current_tip));
        }
        pindex = chainActive[height];
    } else {
        const uint256 hash(ParseHashV(request.params[0], "hash_or_height"));
        pindex = LookupBlockIndex(hash);
        if (!pindex) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
        }
        if (!chainActive.Contains(pindex)) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Block is not in chain %s", Params().NetworkIDString()));
        }
    }
    assert(pindex != nullptr);
    std::set<std::string> stats;
    if (!request.params[1].isNull()) {
        const UniValue stats_univalue = request.params[1].get_array();
        for (unsigned int i = 0; i < stats_univalue.size(); i++) {
            const std::string stat = stats_univalue[i].get_str();