TL;DR: Collections are fantastic. And Polymorphic.

Problems

Null
If Pollution

Solutions

Change the optional attribute to a collection.

Context

If you need to model something that might be missing, some fancy languages will provide optional, nullable, and many other wrong solutions dealing with The Billion Dollar Mistake.

Empty collections and non-empty collections are polymorphic.

Sample Code

Wrong

class Person {
  constructor(name, email) {
    this.name = name;
    this.email = email;
  }

  email() {
    return this.email;
    // might be null    
  }

}

// We cannot use safely person.email()
// We need to check for null explicitly

Right

class Person {
  constructor(name, emails) {
    this.name = name;
    this.emails = emails;
  }

  emails() {
    return this.emails;
  }

  // We can mutate the emails since they are not essential

  addEmail(email) {
    this.emails.push(email);
  }

  removeEmail(email) {
    const index = this.emails.indexOf(email);
    if (index !== -1) {
      this.emails.splice(index, 1);
    }
  }
}

// we can iterate the person.emails() 
// in a loop without checking for null