Prevent making bind param if casted value is nil

If casted value is nil, generated SQL should be `IS NULL`. But currently
it is generated as `= NULL`. To prevent this behavior, avoid making bind
param if casted value is nil.

Fixes #28945.

2 files changed, 7 insertions, 1 deletions

diff --git a/activerecord/test/cases/enum_test.rb b/activerecord/test/cases/enum_test.rb
index db3da53487..4ef9a125e6 100644
--- a/activerecord/test/cases/enum_test.rb
+++ b/activerecord/test/cases/enum_test.rb
@@ -60,6 +60,7 @@ class EnumTest < ActiveRecord::TestCase
     assert_not_equal @book, Book.where(status: [:written]).first
     assert_not_equal @book, Book.where.not(status: :published).first
     assert_equal @book, Book.where.not(status: :written).first
+    assert_equal books(:ddd), Book.where(read_status: :forgotten).first
   end
 
   test "find via where with strings" do
@@ -69,6 +70,7 @@ class EnumTest < ActiveRecord::TestCase
     assert_not_equal @book, Book.where(status: ["written"]).first
     assert_not_equal @book, Book.where.not(status: "published").first
     assert_equal @book, Book.where.not(status: "written").first
+    assert_equal books(:ddd), Book.where(read_status: "forgotten").first
   end
 
   test "build from scope" do
diff --git a/activerecord/test/cases/relation/where_test.rb b/activerecord/test/cases/relation/where_test.rb
index cbc466d6b8..42dae4d569 100644
--- a/activerecord/test/cases/relation/where_test.rb
+++ b/activerecord/test/cases/relation/where_test.rb
@@ -15,7 +15,7 @@ require "models/vertex"
 
 module ActiveRecord
   class WhereTest < ActiveRecord::TestCase
-    fixtures :posts, :edges, :authors, :author_addresses, :binaries, :essays, :cars, :treasures, :price_estimates
+    fixtures :posts, :edges, :authors, :author_addresses, :binaries, :essays, :cars, :treasures, :price_estimates, :topics
 
     def test_where_copies_bind_params
       author = authors(:david)
@@ -48,6 +48,10 @@ module ActiveRecord
       assert_equal [chef], chefs.to_a
     end
 
+    def test_where_with_casted_value_is_nil
+      assert_equal 4, Topic.where(last_read: "").count
+    end
+
     def test_rewhere_on_root
       assert_equal posts(:welcome), Post.rewhere(title: "Welcome to the weblog").first
     end