rs.addArb('mongodb-arbiter:27017')

Error: assert.soon failed: function() {
        var cfg = hostport;

        var local = db.getSiblingDB("local");
        assert(local.system.replset.count() <= 1,
               "error: local.system.replset has unexpected contents");
        var c = local.system.replset.findOne();
        assert(c, "no config object retrievable from local.system.replset");

        const attemptedVersion = c.version++;

        var max = 0;
        for (var i in c.members) {
            // Omit 'newlyAdded' field if it exists in the config.
            delete c.members[i].newlyAdded;
            if (c.members[i]._id > max)
                max = c.members[i]._id;
        }
        if (isString(hostport)) {
            cfg = {_id: max + 1, host: hostport};
            if (arb)
                cfg.arbiterOnly = true;
        } else if (arb == true) {
            throw Error(
                "Expected first parameter to be a host-and-port string of arbiter, but got " +
                tojson(hostport));
        }

        if (cfg._id == null) {
            cfg._id = max + 1;
        }
        c.members.push(cfg);

        res = self._runCmd({replSetReconfig: c});
        if (res === "") {
            // _runCmd caught an exception.
            return true;
        }
        if (res.ok) {
            return true;
        }
        if (res.code === ErrorCodes.ConfigurationInProgress ||
            res.code === ErrorCodes.CurrentConfigNotCommittedYet) {
            return false;  // keep retrying
        }
        if (res.code === ErrorCodes.NewReplicaSetConfigurationIncompatible) {
            // We will retry only if this error was due to our config version being too low.
            const cfgState = local.system.replset.findOne();
            if (cfgState.version >= attemptedVersion) {
                return false;  // keep retrying
            }
        }
        // Take no action on other errors.
        return true;
    } : {
        "ok" : 0,
        "errmsg" : "Reconfig attempted to install a config that would change the implicit default write concern. Use the setDefaultRWConcern command to set a cluster-wide write concern and try the reconfig again.",
        "code" : 103,
        "codeName" : "NewReplicaSetConfigurationIncompatible",
        "$clusterTime" : {
                "clusterTime" : Timestamp(1627634005, 1),
                "signature" : {
                        "hash" : BinData(0,"0HvodHFBd9MboNymy6f1RCY2YZs="),
                        "keyId" : NumberLong("6990612431667986435")
                }
        },
        "operationTime" : Timestamp(1627634005, 1)
} The hang analyzer is automatically called in assert.soon functions. If you are *expecting* assert.soon to possibly fail, call assert.soon with {runHangAnalyzer: false} as the fifth argument (you can fill unused arguments with `undefined`). :
doassert@src/mongo/shell/assert.js:20:14
assert.soon@src/mongo/shell/assert.js:382:17
rs.add@src/mongo/shell/utils.js:1624:5
rs.addArb@src/mongo/shell/utils.js:1696:12
@(shell):1:1