Fatal error: Uncaught Error: Call to a member function dirlist() on null in extension_wbc_importer.php:77 Helper.php

extension_wbc_importer.php

<?php 

public function demoFiles() {
    $this->filesystem = $this->parent->filesystem->execute( 'object' );
    // $dir_array1 = $this->filesystem->dirlist( $this->demo_data_dir, false, true );
    $dir_array = dirToArray($this->demo_data_dir);

    ----

Fatal error: Uncaught Error: Call to a member function dirlist() on null in extension_wbc_importer.php:77 Helper.php

<?php 
function dirToArray($dir) {
   
   $result = array();
   $cdir = scandir($dir);
   foreach ($cdir as $key => $value)
   {
      if (!in_array($value,array(".","..")))
      {
         if (is_dir($dir . DIRECTORY_SEPARATOR . $value))
         {
            $result[$value] = array(
                'name' => $value,
                'type' => 'd',
                'files' => dirToArray($dir . DIRECTORY_SEPARATOR . $value),
            );
         }
         else
         {
            $result[$value] = array(
                'name' => $value,
                'type' => 'f',
            );
         } 
      }
   }
   
   return $result;
}