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"
            "       \"sequence\": n      (numeric) The script sequence number\n"
            "       \"txinwitness\": [\"hex\", ...] (array of string) hex-encoded witness data (if any)\n"
            "     }\n"
            "     ,...\n"
            "  ],\n"
            "  \"vout\" : [              (array of json objects)\n"
            "     {\n"
            "       \"value\" : x.xxx,            (numeric) The value in " + CURRENCY_UNIT + "\n"
            "       \"n\" : n,                    (numeric) index\n"
            "       \"scriptPubKey\" : {          (json object)\n"
            "         \"asm\" : \"asm\",          (string) the asm\n"
            "         \"hex\" : \"hex\",          (string) the hex\n"
            "         \"reqSigs\" : n,            (numeric) The required sigs\n"
            "         \"type\" : \"pubkeyhash\",  (string) The type, eg 'pubkeyhash'\n"
            "         \"addresses\" : [           (json array of string)\n"
            "           \"address\"        (string) bitcoin address\n"
            "           ,...\n"
            "         ]\n"
            "       }\n"
            "     }\n"
            "     ,...\n"
            "  ],\n"
            "  \"blockhash\" : \"hash\",   (string) the block hash\n"
            "  \"confirmations\" : n,      (numeric) The confirmations\n"
            "  \"blocktime\" : ttt         (numeric) The block time in seconds since epoch (Jan 1 1970 GMT)\n"
            "  \"time\" : ttt,             (numeric) Same as \"blocktime\"\n"
            "}\n"
                    },
                },