If I create an RBF transaction using the Qt GUI but specify my own custom change address, bumpfee doesn't work because it claims it can't find the change address:

    "Transaction does not have a change output"

This is because none of the outputs satisfy

    pWallet->IsChange(...)

I see there's a "TODO" commented in `CWallet::IsChange()` in `src/wallet/wallet.cpp`:

    // TODO: fix handling of 'change' outputs. The assumption is that any
    // payment to a script that is ours, but is not in the address book
    // is change.

I tend to put all my addresses in the address book whether I'm going to use them as change or not. I guess if the wallet was capable of creating its own SegWit change addresses I'd stop using custom change addresses, but currently it always seems to send change to a legacy address if I don't manually specify a change address.
{
    UniValue params(UniValue::VOBJ);
    UniValue positional_args{UniValue::VARR};
    for (std::string_view s: strParams) {
        size_t pos = s.find('=');
        if (pos == std::string::npos) {
            positional_args.push_back(rpcCvtTable.ArgToUniValue(s, strMethod, positional_args.size()));
            continue;
        }
        std::string name{s.substr(0, pos)};
        std::string_view value{s.substr(pos+1)};
        
        
        
        params.pushKV(name, rpcCvtTable.ArgToUniValue(value, strMethod, name));
    }
    if (!positional_args.empty()) {
        
        
        
        params.pushKVEnd("args", positional_args);
    }
    return params;
}