Merge pull request #28138 from rwz/rwz/hwia-compact

Make HWIA#compact not return nil when no nils

activesupport/lib/active_support/hash_with_indifferent_access.rb

@@ -270,7 +270,7 @@ def transform_values(*args, &block)
     end
 
     def compact
-      dup.compact!
+      dup.tap(&:compact!)
     end
 
     # Convert to a regular hash with string keys.

activesupport/test/core_ext/hash_ext_test.rb

@@ -597,6 +597,16 @@ def test_indifferent_compact
     assert_equal(@strings, compacted_hash)
     assert_equal(hash_contain_nil_value, hash)
     assert_instance_of ActiveSupport::HashWithIndifferentAccess, compacted_hash
+
+    empty_hash = ActiveSupport::HashWithIndifferentAccess.new
+    compacted_hash = empty_hash.compact
+
+    assert_equal compacted_hash, empty_hash
+
+    non_empty_hash = ActiveSupport::HashWithIndifferentAccess.new(foo: :bar)
+    compacted_hash = non_empty_hash.compact
+
+    assert_equal compacted_hash, non_empty_hash
   end
 
   def test_indifferent_to_hash