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]
```
}
        
        if (input.sighash_type > 0) {
            in.pushKV("sighash", SighashToStr((unsigned char)input.sighash_type));
        }
        
        if (!input.redeem_script.empty()) {
            UniValue r(UniValue::VOBJ);
            ScriptToUniv(input.redeem_script, r, false);
            in.pushKV("redeem_script", r);
        }
        if (!input.witness_script.empty()) {
            UniValue r(UniValue::VOBJ);
            ScriptToUniv(input.witness_script, r, false);
            in.pushKV("witness_script", r);
        }
        
        if (!input.hd_keypaths.empty()) {
            UniValue keypaths(UniValue::VARR);
            for (auto entry : input.hd_keypaths) {
                UniValue keypath(UniValue::VOBJ);
                keypath.pushKV("pubkey", HexStr(entry.first));
                keypath.pushKV("master_fingerprint", strprintf("%08x", ReadBE32(entry.second.fingerprint)));
                keypath.pushKV("path", WriteHDKeypath(entry.second.path));
                keypaths.push_back(keypath);
            }
            in.pushKV("bip32_derivs", keypaths);
        }
        
        if (!input.final_script_sig.empty()) {