travis run: https://travis-ci.org/bitcoin/bitcoin/jobs/406813397

```
rpc_psbt.py failed, Duration: 4 s
stdout:
2018-07-22T13:28:57.765000Z TestFramework (INFO): Initializing test directory /tmp/bitcoin_test_runner_20180722_132530/rpc_psbt_49
2018-07-22T13:29:00.531000Z TestFramework (ERROR): Assertion failed
Traceback (most recent call last):
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/test_framework/test_framework.py", line 160, in main
    self.run_test()
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/rpc_psbt.py", line 101, in run_test
    assert_raises_rpc_error(-22, "TX decode failed", self.nodes[0].converttopsbt, signedtx['hex'])
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/test_framework/util.py", line 105, in assert_raises_rpc_error
    assert try_rpc(code, message, fun, *args, **kwds), "No exception raised"
AssertionError: No exception raised
UniValue txids = request.params[0].get_array();
    for (unsigned int idx = 0; idx < txids.size(); idx++) {
        const UniValue& txid = txids[idx];
        uint256 hash(ParseHashV(txid, "txid"));
        if (setTxids.count(hash))
            throw JSONRPCError(RPC_INVALID_PARAMETER, std::string("Invalid parameter, duplicated txid: ")+txid.get_str());
       setTxids.insert(hash);
       oneTxid = hash;
    }
    CBlockIndex* pblockindex = nullptr;
    uint256 hashBlock;
    if (!request.params[1].isNull()) {
        LOCK(cs_main);
        hashBlock = ParseHashV(request.params[1], "blockhash");
        pblockindex = LookupBlockIndex(hashBlock);
        if (!pblockindex) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
        }
    } else {
        LOCK(cs_main);
        
        for (const auto& tx : setTxids) {
            const Coin& coin = AccessByTxid(*pcoinsTip, tx);
            if (!coin.IsSpent()) {
                pblockindex = chainActive[coin.nHeight];
                break;
            }
        }
    }