title: does ""===null?
body: <p>when comparing string to see if it is empty, is there any difference between:</p>
  
  <pre><code>if($string==NULL){
      //do work
  }
  </code></pre>
  
  <p>and</p>
  
  <pre><code>if($string==""){
      /do work
  }
  </code></pre>
  
  <p>Just wondering beacuse I want to know which one is more effective in detecting blank input.</p>