reverted:
--- b/core/modules/migrate_drupal/config/install/migrate.migration.d6_user.yml
+++ a/core/modules/migrate_drupal/config/install/migrate.migration.d6_user.yml
@@ -23,13 +23,8 @@
     migration: d6_user_role
     source: roles
   user_picture:
+    plugin: d6_user_picture
+    source: uid
-    -
-      plugin: skip_process_on_empty
-      source: picture
-    -
-      plugin: migration
-      migration: d6_user_picture_file
-      source: uid
 destination:
   plugin: entity:user
   md5_passwords: true
reverted:
--- /dev/null
+++ a/core/modules/migrate_drupal/src/Plugin/migrate/process/d6/UserPicture.php
@@ -0,0 +1,63 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\migrate_drupal\Plugin\migrate\process\d6\UserPicture.
+ */
+
+namespace Drupal\migrate_drupal\Plugin\migrate\process\d6;
+
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\Entity\MigrationInterface;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Plugin\MigrateProcessInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * The user picture process plugin.
+ *
+ * @MigrateProcessPlugin(
+ *   id = "d6_user_picture"
+ * )
+ */
+class UserPicture extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The migration plugin.
+   *
+   * @var \Drupal\migrate\Plugin\MigrateProcessInterface
+   */
+  protected $migrationPlugin;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(array $configuration, $plugin_id, array $plugin_definition, MigrationInterface $migration, MigrateProcessInterface $migration_plugin) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->migration = $migration;
+    $this->migrationPlugin = $migration_plugin;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $migration,
+      $container->get('plugin.manager.migrate.process')->createInstance('migration', array('migration' => 'd6_user_picture_file'), $migration)
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    return $row->getSourceProperty('picture') ? $this->migrationPlugin->transform($value, $migrate_executable, $row, $destination_property) : NULL;
+  }
+
+}
only in patch2:
unchanged:
--- a/core/modules/user/migration_templates/d6_user.yml
+++ b/core/modules/user/migration_templates/d6_user.yml
@@ -23,8 +23,14 @@ process:
     migration: d6_user_role
     source: roles
   user_picture:
-    plugin: d6_user_picture
-    source: uid
+    -
+      plugin: skip_on_empty
+      method: process
+      source: picture
+    -
+      plugin: migration
+      migration: d6_user_picture_file
+      source: uid
 destination:
   plugin: entity:user
   md5_passwords: true
only in patch2:
unchanged:
--- a/core/modules/user/src/Plugin/migrate/process/d6/UserPicture.php
+++ /dev/null
@@ -1,63 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\user\Plugin\migrate\process\d6\UserPicture.
- */
-
-namespace Drupal\user\Plugin\migrate\process\d6;
-
-use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
-use Drupal\migrate\Entity\MigrationInterface;
-use Drupal\migrate\MigrateExecutableInterface;
-use Drupal\migrate\Plugin\MigrateProcessInterface;
-use Drupal\migrate\ProcessPluginBase;
-use Drupal\migrate\Row;
-use Symfony\Component\DependencyInjection\ContainerInterface;
-
-/**
- * The user picture process plugin.
- *
- * @MigrateProcessPlugin(
- *   id = "d6_user_picture"
- * )
- */
-class UserPicture extends ProcessPluginBase implements ContainerFactoryPluginInterface {
-
-  /**
-   * The migration plugin.
-   *
-   * @var \Drupal\migrate\Plugin\MigrateProcessInterface
-   */
-  protected $migrationPlugin;
-
-  /**
-   * {@inheritdoc}
-   */
-  public function __construct(array $configuration, $plugin_id, array $plugin_definition, MigrationInterface $migration, MigrateProcessInterface $migration_plugin) {
-    parent::__construct($configuration, $plugin_id, $plugin_definition);
-    $this->migration = $migration;
-    $this->migrationPlugin = $migration_plugin;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
-    return new static(
-      $configuration,
-      $plugin_id,
-      $plugin_definition,
-      $migration,
-      $container->get('plugin.manager.migrate.process')->createInstance('migration', array('migration' => 'd6_user_picture_file'), $migration)
-    );
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
-    return $row->getSourceProperty('picture') ? $this->migrationPlugin->transform($value, $migrate_executable, $row, $destination_property) : NULL;
-  }
-
-}