User.php

<?php

namespace Drupal\user\Plugin\migrate;

use Drupal\migrate\Exception\RequirementsException;
use Drupal\migrate_drupal\Plugin\migrate\FieldMigration;

/**
 * Plugin class for Drupal 7 user migrations dealing with fields and profiles.
 */
class User extends FieldMigration {

  /**
   * {@inheritdoc}
   */
  public function getProcess() {
    if (!$this->init) {
      $this->init = TRUE;
      $this->fieldDiscovery
        ->addEntityFieldProcesses($this, 'user');
      $definition = [
        'source' => [
          'plugin' => 'profile_field',
          'ignore_map' => TRUE,
        ],
        'idMap' => [
          'plugin' => 'null',
        ],
        'destination' => [
          'plugin' => 'null',
        ],
      ];
      try {
        $profile_migration = $this->migrationPluginManager
          ->createStubMigration($definition);

        // Ensure that Profile is enabled in the source DB.
        $profile_migration
          ->checkRequirements();
        foreach ($profile_migration
          ->getSourcePlugin() as $row) {
          $name = $row
            ->getSourceProperty('name');
          $this->process[$name] = $name;
        }
      } catch (RequirementsException $e) {

        // The checkRequirements() call will fail when the profile module does
        // not exist on the source site.
      }
    }
    return parent::getProcess();
  }

}