Make sure to persist a newly-nil serialized value

The subtype will (quite reasonably) ignore the possibility that it has
`changed_in_place?` by becoming nil.

Fixes #19467

1 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/test/cases/serialized_attribute_test.rb b/activerecord/test/cases/serialized_attribute_test.rb
index e29f7462c8..7c92453ee3 100644
--- a/activerecord/test/cases/serialized_attribute_test.rb
+++ b/activerecord/test/cases/serialized_attribute_test.rb
@@ -264,4 +264,14 @@ class SerializedAttributeTest < ActiveRecord::TestCase
       Topic.serialize(:content, Regexp)
     end
   end
+
+  def test_newly_emptied_serialized_hash_is_changed
+    Topic.serialize(:content, Hash)
+    topic = Topic.create(content: { "things" => "stuff" })
+    topic.content.delete("things")
+    topic.save!
+    topic.reload
+
+    assert_equal({}, topic.content)
+  end
 end