title: How to declare a type as nullable in TypeScript?
body: <p>I have an interface in TypeScript.</p>
  
  <pre><code>interface Employee{
      id: number;
      name: string;
      salary: number;
  }
  </code></pre>
  
  <p>I would like to make <code>salary</code> as a nullable field (Like we can do in C#). Is this possible to do in TypeScript?</p>