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 
}
    bool fVerbose = false;
    if (!request.params[1].isNull())
        fVerbose = request.params[1].get_bool();
    uint256 hash = ParseHashV(request.params[0], "parameter 1");
    LOCK(mempool.cs);
    CTxMemPool::txiter it = mempool.mapTx.find(hash);
    if (it == mempool.mapTx.end()) {
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Transaction not in mempool");
    }
    CTxMemPool::setEntries setAncestors;
    uint64_t noLimit = std::numeric_limits<uint64_t>::max();
    std::string dummy;
    mempool.CalculateMemPoolAncestors(*it, setAncestors, noLimit, noLimit, noLimit, noLimit, dummy, false);
    if (!fVerbose) {
        UniValue o(UniValue::VARR);
        for (CTxMemPool::txiter ancestorIt : setAncestors) {
            o.push_back(ancestorIt->GetTx().GetHash().ToString());
        }
        return o;
    } else {
        UniValue o(UniValue::VOBJ);
        for (CTxMemPool::txiter ancestorIt : setAncestors) {
            const CTxMemPoolEntry &e = *ancestorIt;
            const uint256& _hash = e.GetTx().GetHash();
            UniValue info(UniValue::VOBJ);
            entryToJSON(::mempool, info, e);
            o.pushKV(_hash.ToString(), info);
        }
        return o;