No need to cache collection proxies separately

Because merging the association scope was removed.

activerecord/lib/active_record/associations/collection_association.rb

@@ -38,13 +38,7 @@ def reader(force_reload = false)
           reload
         end
 
-        if null_scope?
-          # Cache the proxy separately before the owner has an id
-          # or else a post-save proxy will still lack the id
-          @null_proxy ||= CollectionProxy.create(klass, self)
-        else
-          @proxy ||= CollectionProxy.create(klass, self)
-        end
+        CollectionProxy.create(klass, self)
       end
 
       # Implements the writer method, e.g. foo.items= for Foo.has_many :items

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -611,21 +611,16 @@ def test_finding_using_primary_key
 
   def test_update_all_on_association_accessed_before_save
     firm = Firm.new(name: "Firm")
-    clients_proxy_id = firm.clients.object_id
     firm.clients << Client.first
     firm.save!
     assert_equal firm.clients.count, firm.clients.update_all(description: "Great!")
-    assert_not_equal clients_proxy_id, firm.clients.object_id
   end
 
   def test_update_all_on_association_accessed_before_save_with_explicit_foreign_key
-    # We can use the same cached proxy object because the id is available for the scope
     firm = Firm.new(name: "Firm", id: 100)
-    clients_proxy_id = firm.clients.object_id
     firm.clients << Client.first
     firm.save!
     assert_equal firm.clients.count, firm.clients.update_all(description: "Great!")
-    assert_equal clients_proxy_id, firm.clients.object_id
   end
 
   def test_belongs_to_sanity

activerecord/test/cases/associations_test.rb

@@ -233,11 +233,6 @@ def test_scoped_allows_conditions
     assert_equal david.projects, david.projects.scope
   end
 
-  test "proxy object is cached" do
-    david = developers(:david)
-    assert david.projects.equal?(david.projects)
-  end
-
   test "inverses get set of subsets of the association" do
     man = Man.create
     man.interests.create