title: Fatal error: Cannot use isset() on the result of an expression
body: <p>When coding with <code>isset</code> i am getting an fatal error.I have searched stackoverflow but results are not satisfactory.</p>
  
  <p>I am getting </p>
  
  <blockquote>
    <p>Fatal error: Cannot use isset() on the result of an expression (you can use "null !== expression" instead)</p>
  </blockquote>
  
  <p><strong>My codes are</strong></p>
  
  <pre><code>if (!isset( $size || $color )) {
      $style = '';    
  }else{
      $style = 'font-size : ' . $size . ';color:' . $color;   
  }
  </code></pre>