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
std::set<int> setSubtractFeeFromOutputs;
    if (!options.isNull()) {
      if (options.type() == UniValue::VBOOL) {
        
        coinControl.fAllowWatchOnly = options.get_bool();
      }
      else {
        RPCTypeCheckArgument(options, UniValue::VOBJ);
        RPCTypeCheckObj(options,
            {
                {"changeAddress", UniValueType(UniValue::VSTR)},
                {"changePosition", UniValueType(UniValue::VNUM)},
                {"change_type", UniValueType(UniValue::VSTR)},
                {"includeWatching", UniValueType(UniValue::VBOOL)},
                {"lockUnspents", UniValueType(UniValue::VBOOL)},
                {"feeRate", UniValueType()}, 
                {"subtractFeeFromOutputs", UniValueType(UniValue::VARR)},
                {"replaceable", UniValueType(UniValue::VBOOL)},
                {"conf_target", UniValueType(UniValue::VNUM)},
                {"estimate_mode", UniValueType(UniValue::VSTR)},
            },
            true, true);
        if (options.exists("changeAddress")) {
            CTxDestination dest = DecodeDestination(options["changeAddress"].get_str());
            if (!IsValidDestination(dest)) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "changeAddress must be a valid bitcoin address");
            }
            coinControl.destChange = dest;
        }
        if (options.exists("changePosition"))