title: Why does var foo = null compile
body: <p>I am starting with Kotlin and trying to understand something.</p>
  
  <p><code>var foo: String = null</code> does not compile as expected.</p>
  
  <p><code>var foo: String? = null</code> should be the correct syntax and compile as expected.</p>
  
  <p>So why does <code>var foo = null</code> compile??</p>