Followup of #15771

Make sure we handle explicitly passed nil's to lock_version as well.
An explicitly passed nil value is now converted to 0 on LockingType,
so that we don't end up with ActiveRecord::StaleObjectError in update record
optimistic locking

Fixes #24695

activerecord/lib/active_record/locking/optimistic.rb

@@ -190,6 +190,10 @@ def deserialize(value)
         super.to_i
       end
 
+      def serialize(value)
+        super.to_i
+      end
+
       def init_with(coder)
         __setobj__(coder['subtype'])
       end

activerecord/test/cases/locking_test.rb

@@ -169,6 +169,12 @@ def test_lock_new_with_nil
     assert_equal 1, p1.lock_version
   end
 
+  def test_lock_new_when_explicitly_passing_nil
+    p1 = Person.new(:first_name => 'anika', lock_version: nil)
+    p1.save!
+    assert_equal 0, p1.lock_version
+  end
+
   def test_touch_existing_lock
     p1 = Person.find(1)
     assert_equal 0, p1.lock_version