RPC bumpfee with an explicit feerate using `conf_target` and `estimate_mode` errors with `JSONRPCException: JSON integer out of range (-1)`.
case Type::OBJ_USER_KEYS: {
            ret += "json object";
            break;
        }
        case Type::ARR: {
            ret += "json array";
            break;
        }
        } 
    }
    if (m_fallback.which() == 1) {
        ret += ", optional, default=" + boost::get<std::string>(m_fallback);
    } else {
        switch (boost::get<RPCArg::Optional>(m_fallback)) {
        case RPCArg::Optional::OMITTED: {
            
            break;
        }
        case RPCArg::Optional::OMITTED_NAMED_ARG: {
            ret += ", optional"; 
            break;
        }
        case RPCArg::Optional::NO: {
            ret += ", required";
            break;
        }
        } 
    }
    ret += ")";
    ret += m_description.empty() ? "" : " " + m_description;