Filter scalar values when params permit hashes or arrays

This brings the behavior more inline with other similar cases, such as
receiving a hash when an array of scalars was expected. Prior to this
commit, the key would be present, but the value would be `nil`

actionpack/lib/action_controller/metal/strong_parameters.rb

@@ -756,6 +756,10 @@ def array_of_permitted_scalars?(value)
         end
       end
 
+      def non_scalar?(value)
+        value.is_a?(Array) || value.is_a?(Parameters)
+      end
+
       EMPTY_ARRAY = []
       def hash_filter(params, filter)
         filter = filter.with_indifferent_access
@@ -770,7 +774,7 @@ def hash_filter(params, filter)
             array_of_permitted_scalars?(self[key]) do |val|
               params[key] = val
             end
-          else
+          elsif non_scalar?(value)
             # Declaration { user: :name } or { user: [:name, :age, { address: ... }] }.
             params[key] = each_element(value) do |element|
               element.permit(*Array.wrap(filter[key]))

actionpack/test/controller/parameters/parameters_permit_test.rb

@@ -360,4 +360,13 @@ def dup; @dupped = true; end
     assert @params.include? 'person'
     assert_not @params.include? :gorilla
   end
+
+  test "scalar values should be filtered when array or hash is specified" do
+    params = ActionController::Parameters.new(foo: "bar")
+
+    assert params.permit(:foo).has_key?(:foo)
+    refute params.permit(foo: []).has_key?(:foo)
+    refute params.permit(foo: [:bar]).has_key?(:foo)
+    refute params.permit(foo: :bar).has_key?(:foo)
+  end
 end