fix exception on polymorphic associations with predicates

activerecord/lib/active_record/association_relation.rb

@@ -8,7 +8,15 @@ def initialize(klass, table, association)
     def proxy_association
       @association
     end
+    
+    def size
+      @association.size
+    end
 
+    def empty?
+      @association.empty?
+    end
+        
     private
 
     def exec_queries

activerecord/test/cases/associations/eager_test.rb

@@ -1197,7 +1197,15 @@ def test_deep_including_through_habtm
     author = Author.includes(:posts).references(:posts).reorder(:name).find_by('posts.title IS NOT NULL')
     assert_equal authors(:bob), author
   end
+  
+  test "preloading with a polymorphic association and using the existential predicate but also using a select" do
+    assert_equal authors(:david), authors(:david).essays.includes(:writer).first.writer
 
+    assert_nothing_raised do
+      authors(:david).essays.includes(:writer).select(:name).any?
+    end
+  end
+  
   test "preloading with a polymorphic association and using the existential predicate" do
     assert_equal authors(:david), authors(:david).essays.includes(:writer).first.writer