I can't understand what is the problem with this code?

import cassandra from "cassandra-driver";

class Cass {
static _cass : cassandra.Client;

  this._cass = new cassandra.Client({
    contactPoints: ['localhost'],
    localDataCenter: 'datacenter1',
    keyspace: 'ks1'
  });
}

I get the following error at this._cass assignment line:

Unexpected token. A constructor, method, accessor, or property was expected.ts(1068) Object is possibly 'undefined'.

EDIT I have a similar class like following that work with no problem, and I am wondering to know why? What is the difference between this class and the previous one?

import mysql from "mysql2";
import { Pool } from "mysql2/promise";

class Pools {
  static _pools: Pool;

  static connect(options: mysql.PoolOptions) {
    this._pools = mysql.createPool(options).promise();
    this._pools.execute('SELECT 1 + 1;');
  }

  static close() {
    this._pools.end();
  }

  static execute(sql: string, params?: any[] | undefined) {
    return this._pools.execute(sql, params);
  }
}


export { Pools };