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 
"    \"depends\" : [           (array) unconfirmed transactions used as inputs for this transaction\n"
           "        \"transactionid\",    (string) parent transaction id\n"
           "       ... ]\n"
           "    \"spentby\" : [           (array) unconfirmed transactions spending outputs from this transaction\n"
           "        \"transactionid\",    (string) child transaction id\n"
           "       ... ]\n"
           "    \"bip125-replaceable\" : true|false,  (boolean) Whether this transaction could be replaced due to BIP125 (replace-by-fee)\n";
}
static void entryToJSON(const CTxMemPool& pool, UniValue& info, const CTxMemPoolEntry& e) EXCLUSIVE_LOCKS_REQUIRED(pool.cs)
{
    AssertLockHeld(pool.cs);
    UniValue fees(UniValue::VOBJ);
    fees.pushKV("base", ValueFromAmount(e.GetFee()));
    fees.pushKV("modified", ValueFromAmount(e.GetModifiedFee()));
    fees.pushKV("ancestor", ValueFromAmount(e.GetModFeesWithAncestors()));
    fees.pushKV("descendant", ValueFromAmount(e.GetModFeesWithDescendants()));
    info.pushKV("fees", fees);
    info.pushKV("size", (int)e.GetTxSize());
    info.pushKV("fee", ValueFromAmount(e.GetFee()));
    info.pushKV("modifiedfee", ValueFromAmount(e.GetModifiedFee()));
    info.pushKV("time", e.GetTime());
    info.pushKV("height", (int)e.GetHeight());
    info.pushKV("descendantcount", e.GetCountWithDescendants());
    info.pushKV("descendantsize", e.GetSizeWithDescendants());
    info.pushKV("descendantfees", e.GetModFeesWithDescendants());
    info.pushKV("ancestorcount", e.GetCountWithAncestors());
    info.pushKV("ancestorsize", e.GetSizeWithAncestors());
    info.pushKV("ancestorfees", e.GetModFeesWithAncestors());
    info.pushKV("wtxid", pool.vTxHashes[e.vTxHashesIdx].first.ToString());
    const CTransaction& tx = e.GetTx();