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]
```
"      },\n"
            "      \"partial_signatures\" : {             (json object, optional)\n"
            "        \"pubkey\" : \"signature\",           (string) The public key and signature that corresponds to it.\n"
            "        ,...\n"
            "      }\n"
            "      \"sighash\" : \"type\",                  (string, optional) The sighash type to be used\n"
            "      \"redeem_script\" : {       (json object, optional)\n"
            "          \"asm\" : \"asm\",            (string) The asm\n"
            "          \"hex\" : \"hex\",            (string) The hex\n"
            "          \"type\" : \"pubkeyhash\",    (string) The type, eg 'pubkeyhash'\n"
            "        }\n"
            "      \"witness_script\" : {       (json object, optional)\n"
            "          \"asm\" : \"asm\",            (string) The asm\n"
            "          \"hex\" : \"hex\",            (string) The hex\n"
            "          \"type\" : \"pubkeyhash\",    (string) The type, eg 'pubkeyhash'\n"
            "        }\n"
            "      \"bip32_derivs\" : {          (json object, optional)\n"
            "        \"pubkey\" : {                     (json object, optional) The public key with the derivation path as the value.\n"
            "          \"master_fingerprint\" : \"fingerprint\"     (string) The fingerprint of the master key\n"
            "          \"path\" : \"path\",                         (string) The path\n"
            "        }\n"
            "        ,...\n"
            "      }\n"
            "      \"final_scriptsig\" : {       (json object, optional)\n"
            "          \"asm\" : \"asm\",            (string) The asm\n"
            "          \"hex\" : \"hex\",            (string) The hex\n"
            "        }\n"
            "       \"final_scriptwitness\": [\"hex\", ...] (array of string) hex-encoded witness data (if any)\n"
            "      \"unknown\" : {                (json object) The unknown global fields\n"
            "        \"key\" : \"value\"            (key-value pair) An unknown key-value pair\n"