title: Wordpress Fatal error: Can't use function return value in write context
body: <p>I have recently acquired a new client and migrated his website from the original developers hosting to his own hosting.  Prior to transferring to the new hosting, the site was working fine.  However, now i get the following error:</p>
  
  <p>Fatal error: Can't use function return value in write context in /home/agingtree/public_html/dev/wp-content/themes/aging-tree/lib/vendor.php on line 55</p>
  
  <p>Nothing has been modified other than the db to reflect the new domain and location etc.  Here is the code around the issue that is showing.  Any help is appreciated:</p>
  
  <pre><code> /*
   * Vendor Query Vars
   */
  add_filter('query_vars', 'vendor_query_vars');
  
  function vendor_query_vars($vars){
      $vars[] = "vendor";
      $vars[] = "service-category";
      $vars[] = "service-subcategory";
      $vars[] = "city";
      $vars[] = "zip";
      return $vars;
  }
  
  /*
   * Vendor API Cache
   */
  add_action('pre_get_posts', 'vendor_api_cache');
  
  function vendor_api_cache(){
      if (!empty (get_query_var('vendor'))):
  
          $data = api_get('vendor',['id' =&gt; get_query_var('vendor')]);
          if(!empty($data[0])){
              $vendor = $data[0];
          }
          else{
              $vendor = null;
          }
  
          wp_cache_set('vendor',$vendor);
  
      endif;
  }
  </code></pre>