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
RPCTypeCheck(request.params, {
        UniValue::VSTR,
        UniValueType(), 
    });
    
    CMutableTransaction mtx;
    if (!DecodeHexTx(mtx, request.params[0].get_str()))
        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
    CTransactionRef tx(MakeTransactionRef(std::move(mtx)));
    CAmount max_raw_tx_fee = DEFAULT_MAX_RAW_TX_FEE;
    
    if (request.params[1].isBool()) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Second argument must be numeric (maxfeerate) and no longer supports a boolean. To allow a transaction with high fees, set maxfeerate to 0.");
    } else if (!request.params[1].isNull()) {
        size_t weight = GetTransactionWeight(*tx);
        CFeeRate fr(AmountFromValue(request.params[1]));
        
        
        
        max_raw_tx_fee = fr.GetFee((weight+3)/4);
    }
    uint256 txid;
    std::string err_string;
    const TransactionError err = BroadcastTransaction(tx, txid, err_string, max_raw_tx_fee);
    if (TransactionError::OK != err) {
        throw JSONRPCTransactionError(err, err_string);
    }
    return txid.GetHex();
}
static UniValue testmempoolaccept(const JSONRPCRequest& request)