Explain on mongos with readPref:secondary fails in a wrong way when can't match the read pref

mongos> db.getMongo().setReadPref('secondary')

mongos> db.test.find().explain()

2019-09-20T10:39:20.947-0500 E QUERY    [js] Error: explain failed: {

	"ok" : 0,

	"errmsg" : "Explain command on shard db1/localhost:27030 failed, caused by: { ok: 1.0 }",

	"code" : 96,

	"codeName" : "OperationFailed",

	"operationTime" : Timestamp(1568993960, 1),

	"$clusterTime" : {

		"clusterTime" : Timestamp(1568993960, 1),

		"signature" : {

			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),

			"keyId" : NumberLong(0)

		}

	}

}

   OperationContext* opCtx, const std::vector<AsyncRequestsSender::Response>& responses) {

    std::vector<Strategy::CommandResult> results;

    for (auto& response : responses) {

        Status status = Status::OK();

        if (response.swResponse.isOK()) {

            auto& result = response.swResponse.getValue().data;

            status = getStatusFromCommandResult(result);

            if (status.isOK()) {

                invariant(response.shardHostAndPort);

                results.emplace_back(

                    response.shardId, ConnectionString(*response.shardHostAndPort), result);

                continue;

            }

        }

/////////////////// need to add this ------->

        else status = response.swResponse.getStatus();

///////////////////

        // Convert the error status back into the format of a command result.

        BSONObjBuilder statusObjBob;

        CommandHelpers::appendCommandStatusNoThrow(statusObjBob, status);

        // Get the Shard object in order to get the ConnectionString.

        auto shard =

            uassertStatusOK(Grid::get(opCtx)->shardRegistry()->getShard(opCtx, response.shardId));

        results.emplace_back(response.shardId, shard->getConnString(), statusObjBob.obj());

    }

    return results;

}