试试这个：

let users = await this.conn.getRepository(UserEntity)
.createQueryBuilder('user')
.where(search !== null ? 
    'user.firstName LIKE :search': 'TRUE', {search: dto.search})
.getMany();

或者另一种没有“where true”的方法是：

let users = this.conn.getRepository(UserEntity)
.createQueryBuilder('user');
users = search !== null ? users.where('user.firstName LIKE :search',{search: dto.search}) : users
users = await users.getMany();

const query = this.conn
  .getRepository(UserEntity)
  .createQueryBuilder("user");

// Optionally add where condition
if(dto.search){
  query.where("user.firstName LIKE :search", { search: dto.search })
}
// run query
let users = await query.getMany();

一定要注意那些会绊倒if语句的错误值。