Running master 4d661ba:
```
src/bitcoin-cli combinepsbt [""] or src/bitcoin-cli combinepsbt []
```

```
  * frame #0: 0x000000010016054a bitcoind`PartiallySignedTransaction::PartiallySignedTransaction(PartiallySignedTransaction const&) [inlined] boost::optional_detail::optional_base<CMutableTransaction>::is_initialized(this=0x0000000000000000) const at optional.hpp:394 [opt]
    frame #1: 0x000000010016054a bitcoind`PartiallySignedTransaction::PartiallySignedTransaction(PartiallySignedTransaction const&) [inlined] boost::optional_detail::optional_base<CMutableTransaction>::optional_base(this=<unavailable>, rhs=0x0000000000000000) at optional.hpp:196 [opt]
    frame #2: 0x0000000100160542 bitcoind`PartiallySignedTransaction::PartiallySignedTransaction(PartiallySignedTransaction const&) [inlined] boost::optional<CMutableTransaction>::optional(this=0x000070000b9fe7c0, (null)=0x0000000000000000) at optional.hpp:958 [opt]
    frame #3: 0x0000000100160542 bitcoind`PartiallySignedTransaction::PartiallySignedTransaction(PartiallySignedTransaction const&) [inlined] boost::optional<CMutableTransaction>::optional(this=0x000070000b9fe7c0, (null)=0x0000000000000000) at optional.hpp:958 [opt]
    frame #4: 0x0000000100160542 bitcoind`PartiallySignedTransaction::PartiallySignedTransaction(this=0x000070000b9fe7c0, psbt_in=0x0000000000000000) at sign.h:576 [opt]
    frame #5: 0x0000000100142ae5 bitcoind`combinepsbt(JSONRPCRequest const&) [inlined] PartiallySignedTransaction::PartiallySignedTransaction(this=0x000070000b9fe700, psbt_in=<unavailable>) at sign.h:576 [opt]
    frame #6: 0x0000000100142ae0 bitcoind`combinepsbt(request=<unavailable>) at rawtransaction.cpp:1526 [opt]
    frame #7: 0x0000000100170f0a bitcoind`CRPCTable::execute(this=<unavailable>, request=0x000070000b9fead0) const at server.cpp:557 [opt]
```
RPCExamples{
                    HelpExampleCli("signrawtransactionwithkey", "\"myhex\"")
            + HelpExampleRpc("signrawtransactionwithkey", "\"myhex\"")
                },
            }.ToString());
    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VARR, UniValue::VARR, UniValue::VSTR}, true);
    CMutableTransaction mtx;
    if (!DecodeHexTx(mtx, request.params[0].get_str(), true)) {
        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
    }
    CBasicKeyStore keystore;
    const UniValue& keys = request.params[1].get_array();
    for (unsigned int idx = 0; idx < keys.size(); ++idx) {
        UniValue k = keys[idx];
        CKey key = DecodeSecret(k.get_str());
        if (!key.IsValid()) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key");
        }
        keystore.AddKey(key);
    }
    return SignTransaction(*g_rpc_interfaces->chain, mtx, request.params[2], &keystore, true, request.params[3]);
}
UniValue signrawtransaction(const JSONRPCRequest& request)
{
    
    
    throw JSONRPCError(RPC_METHOD_DEPRECATED, "signrawtransaction was removed in v0.18.\n"
        "Clients should transition to using signrawtransactionwithkey and signrawtransactionwithwallet");
}
static UniValue sendrawtransaction(const JSONRPCRequest& request)