Currently, the multisig descriptor constructions are limited to 16 keys only possibly because of template parsing reasons. Under p2sh context, such scripts would be invalid anyway because of 520-byte rule, but we can support up to 20 keys for CHECKMULTISIG in witness script context. 


if (arg.m_fallback.index() == 2) {
            const RPCArg::Type type = arg.m_type;
            switch (std::get<RPCArg::Default>(arg.m_fallback).getType()) {
            case UniValue::VOBJ:
                CHECK_NONFATAL(type == RPCArg::Type::OBJ);
                break;
            case UniValue::VARR:
                CHECK_NONFATAL(type == RPCArg::Type::ARR);
                break;
            case UniValue::VSTR:
                CHECK_NONFATAL(type == RPCArg::Type::STR || type == RPCArg::Type::STR_HEX || type == RPCArg::Type::AMOUNT);
                break;
            case UniValue::VNUM:
                CHECK_NONFATAL(type == RPCArg::Type::NUM || type == RPCArg::Type::AMOUNT || type == RPCArg::Type::RANGE);
                break;
            case UniValue::VBOOL:
                CHECK_NONFATAL(type == RPCArg::Type::BOOL);
                break;
            case UniValue::VNULL:
                
                break;
            default:
                CHECK_NONFATAL(false);
                break;
            }
        }
    }
}
std::string RPCResults::ToDescriptionString() const