title: C# What happens when you pass null to an optional argument
body: <p>If I have a function with an optional argument like so:</p>
  
  <pre><code>public string testFunction (string arg1 = "Adam"){
      return "Hello " + arg1;
  }
  </code></pre>
  
  <p>If I pass a null string to the function, will the function return:</p>
  
  <p>"Hello Adam"</p>
  
  <p>Or:</p>
  
  <p>"Hello " (Hello <em>null</em>)</p>