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]
```
{"proof", RPCArg::Type::STR_HEX,  false,  "", "The hex-encoded proof generated by gettxoutproof"},
                },
                RPCResult{
            "[\"txid\"]      (array, strings) The txid(s) which the proof commits to, or empty array if the proof can not be validated.\n"
                },
                RPCExamples{""},
            }.ToString()
        );
    CDataStream ssMB(ParseHexV(request.params[0], "proof"), SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS);
    CMerkleBlock merkleBlock;
    ssMB >> merkleBlock;
    UniValue res(UniValue::VARR);
    std::vector<uint256> vMatch;
    std::vector<unsigned int> vIndex;
    if (merkleBlock.txn.ExtractMatches(vMatch, vIndex) != merkleBlock.header.hashMerkleRoot)
        return res;
    LOCK(cs_main);
    const CBlockIndex* pindex = LookupBlockIndex(merkleBlock.header.GetHash());
    if (!pindex || !chainActive.Contains(pindex) || pindex->nTx == 0) {
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found in chain");
    }
    
    if (pindex->nTx == merkleBlock.txn.GetNumTransactions()) {
        for (const uint256& hash : vMatch) {
            res.push_back(hash.GetHex());
        }
    }
    return res;
}
CMutableTransaction ConstructTransaction(const UniValue& inputs_in, const UniValue& outputs_in, const UniValue& locktime, const UniValue& rbf)