title: In PHP, what is the differences between NULL and setting a string to equal 2 single quotes
body: <p>I used to set things like this when I wanted blank values.</p>
  
  <pre><code>$blankVar = '';
  </code></pre>
  
  <p>Then after some months, I decided this looked better and had a clearer intent.</p>
  
  <pre><code>$blankVar = null;
  </code></pre>
  
  <p>This worked without hiccup for a while, but recently with a PDO prepared statements I ran into a problem. Binding a value to null made the query fail, whilst binding it to '' did not. I needed to bind it to null, so that if a condition was met, it would insert blank data.</p>
  
  <p>What are the differences between the 2? I still think equaling null (or at least a constant) looks better, so should I do this?</p>
  
  <pre><code>define('EMPTY', '');
  </code></pre>