title: Is a property default value of null the same as no default value?
body: <p>And can I therefore safely refactor all instances of</p>
  
  <pre><code>class Blah
  {
      // ...
      private $foo = null;
      // ...
  }
  </code></pre>
  
  <p>to</p>
  
  <pre><code>class Blah
  {
      // ...
      private $foo;
      // ...
  }
  </code></pre>
  
  <p>?</p>