title: PHP decrement NULL value issue
body: <p>I have noticed if a value is <code>null</code> i can increment it by one using <code>++$value</code> but its not true about decrement , meaning <code>--$value</code> would return <code>null</code> , why?</p>
  
  <pre><code>$value = null;
  echo ++$value; // 1
  echo --$value; // null (I'm expecting -1)
  </code></pre>