uassert(
                28528,
                str::stream() << "Argument to listIndexes must be of type String, not "
                              << typeName(first.type()),
                first.type() == String);
            const NamespaceString ns(parseNs(dbname, cmdObj));
            uassert(
                28529,
                str::stream() << "Argument to listIndexes must be a collection name, "
                              << "not the empty string",
                !ns.coll().empty());

        else if (status != ErrorCodes::NoSuchKey) {
            // NoSuchKey means we have no $voter-tagged nodes in this config;
            // other errors are unexpected.
            fassert(28528, status);
        }

        // $stepDownCheck: one electable node plus ourselves
        pattern = _tagConfig.makePattern();
        status = _tagConfig.addTagCountConstraintToPattern(&pattern,
                                                           MemberConfig::kInternalElectableTagName,
                                                           2);
        if (status.isOK()) {
            _customWriteConcernModes[kStepDownCheckWriteConcernModeName] = pattern;
        }
        else if (status != ErrorCodes::NoSuchKey) {
            // NoSuchKey means we have no $electable-tagged nodes in this config;
            // other errors are unexpected
            fassert(28529, status);
        }