title: What to pass for TypeScript optional parameter when there is no exact value to specify, 'undefined' or 'null'?
body: <p>I have below function in TypeScript (which i can't change the order of the parameters),</p>
  
  <pre><code>user(firstName: string, lastName?: string, address?: string);
  </code></pre>
  
  <p>When in the case where I need to only pass <code>firstName</code> and <code>address</code> what is the better/suitable/recommended value to pass as the <code>lastname</code> ?</p>
  
  <pre><code>case 1: user("Jack", undefined, "NY");
  </code></pre>
  
  <p>or</p>
  
  <pre><code>case 2: user("Jack", null, "NY");
  </code></pre>
  
  <p>What are the pros and cons of each approach ?</p>