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 
{
    UniValue result(UniValue::VOBJ);
    result.pushKV("hash", blockindex->GetBlockHash().GetHex());
    const CBlockIndex* pnext;
    int confirmations = ComputeNextBlockAndDepth(tip, blockindex, pnext);
    result.pushKV("confirmations", confirmations);
    result.pushKV("height", blockindex->nHeight);
    result.pushKV("version", blockindex->nVersion);
    result.pushKV("versionHex", strprintf("%08x", blockindex->nVersion));
    result.pushKV("merkleroot", blockindex->hashMerkleRoot.GetHex());
    result.pushKV("time", (int64_t)blockindex->nTime);
    result.pushKV("mediantime", (int64_t)blockindex->GetMedianTimePast());
    result.pushKV("nonce", (uint64_t)blockindex->nNonce);
    result.pushKV("bits", strprintf("%08x", blockindex->nBits));
    result.pushKV("difficulty", GetDifficulty(blockindex));
    result.pushKV("chainwork", blockindex->nChainWork.GetHex());
    result.pushKV("nTx", (uint64_t)blockindex->nTx);
    if (blockindex->pprev)
        result.pushKV("previousblockhash", blockindex->pprev->GetBlockHash().GetHex());
    if (pnext)
        result.pushKV("nextblockhash", pnext->GetBlockHash().GetHex());
    return result;
}
UniValue blockToJSON(const CBlock& block, const CBlockIndex* tip, const CBlockIndex* blockindex, bool txDetails)