There is no need to check null_relation? in empty_scope?

`values[:extending]` includes `NullRelation` if `null_relation?`.

activerecord/lib/active_record/relation.rb

@@ -689,7 +689,7 @@ module ActiveRecord
     end
 
     def empty_scope? # :nodoc:
-      !null_relation? && @values == klass.unscoped.values
+      @values == klass.unscoped.values
     end
 
     def has_limit_or_offset? # :nodoc:

activerecord/test/cases/relation_test.rb

@@ -101,6 +101,9 @@ module ActiveRecord
 
       relation.merge!(relation)
       assert_predicate relation, :empty_scope?
+
+      assert_not_predicate NullPost.all, :empty_scope?
+      assert_not_predicate FirstPost.all, :empty_scope?
     end
 
     def test_bad_constants_raise_errors

activerecord/test/models/post.rb

@@ -203,6 +203,10 @@ end
 
 class SubAbstractStiPost < AbstractStiPost; end
 
+class NullPost < Post
+  default_scope { none }
+end
+
 class FirstPost < ActiveRecord::Base
   self.inheritance_column = :disabled
   self.table_name = "posts"