Ignore empty condition on #construct_relation_for_exists

At https://github.com/rails/rails/commit/fc0e3354af7e7878bdd905a95ce4c1491113af9a,

```rb
relation = relation.where(conditions)
```

was rewritten to:

```rb
relation.where!(condition)
```

This change accidentally changed the result of `Topic.exists?({})` from true to false.

To fix this regression, first I moved the blank check logic (`opts.blank?`) from `#where` to `#where!`,
because I thought `#where!` should be identical to `#where`, except that instead of returning a new relation,
it adds the condition to the existing relation.

But on second thought after some discussion on https://github.com/rails/rails/pull/34329,
I started to think that just fixing `#construct_relation_for_exists` is more preferable
than changing `#where` and `#where!`.

1 files changed, 1 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 6f420fe6bb..afaa900442 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -363,7 +363,7 @@ module ActiveRecord
 
         case conditions
         when Array, Hash
-          relation.where!(conditions)
+          relation.where!(conditions) unless conditions.empty?
         else
           relation.where!(primary_key => conditions) unless conditions == :none
         end