don't mutate hash with fetch

1 files changed, 6 insertions, 0 deletions

diff --git a/actionpack/test/controller/parameters/parameters_permit_test.rb b/actionpack/test/controller/parameters/parameters_permit_test.rb
index 84e007b5d0..b60c5f058d 100644
--- a/actionpack/test/controller/parameters/parameters_permit_test.rb
+++ b/actionpack/test/controller/parameters/parameters_permit_test.rb
@@ -147,6 +147,12 @@ class ParametersPermitTest < ActiveSupport::TestCase
     assert_equal :foo, e.param
   end
 
+  test "fetch with a default value of a hash does not mutate the object" do
+    params = ActionController::Parameters.new({})
+    params.fetch :foo, {}
+    assert_equal nil, params[:foo]
+  end
+
   test "fetch doesnt raise ParameterMissing exception if there is a default" do
     assert_equal "monkey", @params.fetch(:foo, "monkey")
     assert_equal "monkey", @params.fetch(:foo) { "monkey" }