commit 93810d108bd22cebd6101fb6d8ca20888833cc83
Author: Matthew Radcliffe <mradcliffe@softpixel.com>
Date:   Sat Jul 12 14:04:28 2014 -0400

    Issue #2279395 by mradcliffe, webchick: Rewrite comment to accurately reflect the change.

diff --git a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
index 5638c71..02ef7be 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
@@ -720,8 +720,8 @@ protected function doSave($id, EntityInterface $entity) {
         ->fields((array) $record)
         ->execute();
       // Even if this is a new entity the ID key might have been set, in which
-      // case we should not override the provided ID. An empty value for the
-      // ID is interpreted as NULL and thus overridden.
+      // case we should not override the provided ID. An ID key that is not set
+      // to any value is interpreted as NULL (or DEFAULT) and thus overridden.
       if (!isset($record->{$this->idKey})) {
         $record->{$this->idKey} = $insert_id;
       }