diff --git a/core/lib/Drupal/Core/Entity/RevisionableSchemaConverter.php b/core/lib/Drupal/Core/Entity/RevisionableSchemaConverter.php
index 6b36e34..2d58dd1 100644
--- a/core/lib/Drupal/Core/Entity/RevisionableSchemaConverter.php
+++ b/core/lib/Drupal/Core/Entity/RevisionableSchemaConverter.php
@@ -67,9 +67,9 @@ public function copyData(EntityTypeInterface $entity_type, array &$sandbox) {
       $sandbox['progress'] = 0;
       $sandbox['current_id'] = 0;
       $sandbox['max'] = $this->database->select($base_table)
-          ->countQuery()
-          ->execute()
-          ->fetchField();
+        ->countQuery()
+        ->execute()
+        ->fetchField();
     }
 
     /** @var \Drupal\Core\Entity\Sql\TableMappingInterface $table_mapping */
@@ -114,7 +114,7 @@ public function copyData(EntityTypeInterface $entity_type, array &$sandbox) {
           ->condition($id, $record[$id])
           ->execute()
           ->fetchAll();
-        if (isset($exists) && isset($exists[0]) && ($exists[0]->{$id} == $record[$id])) {
+        if ($exists && isset($exists[0]) && ($exists[0]->{$id} == $record[$id])) {
           $this->database
             ->update($table_name)
             ->fields($values)
diff --git a/core/lib/Drupal/Core/Entity/RevisionableSchemaConverterInterface.php b/core/lib/Drupal/Core/Entity/RevisionableSchemaConverterInterface.php
index 0b21238..41d7bab 100644
--- a/core/lib/Drupal/Core/Entity/RevisionableSchemaConverterInterface.php
+++ b/core/lib/Drupal/Core/Entity/RevisionableSchemaConverterInterface.php
@@ -8,6 +8,7 @@
    * Converts the schema to be revisionable.
    *
    * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type to convert.
    */
   public function convertSchema(EntityTypeInterface $entity_type);
 
@@ -15,7 +16,9 @@ public function convertSchema(EntityTypeInterface $entity_type);
    * Copies existing data to new tables.
    *
    * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type for the data that needs copying.
    * @param array $sandbox
+   *   The sandbox array from hook_update().
    */
   public function copyData(EntityTypeInterface $entity_type, array &$sandbox);
 
diff --git a/core/tests/Drupal/Tests/Core/Entity/RevisionableSchemaConverterTest.php b/core/tests/Drupal/Tests/Core/Entity/RevisionableSchemaConverterTest.php
index 7cfaa9f..16f1c1e 100644
--- a/core/tests/Drupal/Tests/Core/Entity/RevisionableSchemaConverterTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/RevisionableSchemaConverterTest.php
@@ -15,7 +15,7 @@ class RevisionableSchemaConverterTest extends UpdatePathTestBase {
    * @inheritDoc
    */
   protected function setDatabaseDumpFiles() {
-    $this->databaseDumpFiles = [__DIR__ . '/../../../../../modules/system/tests/fixtures/update/drupal-8.bare.standard.php.gz'];
+    $this->databaseDumpFiles = [__DIR__ . '/../../../../../modules/system/tests/fixtures/update/drupal-8.filled.standard.php.gz'];
   }
 
   public function testMakeRevisionable() {