fix(products): tolerate explicit null values on filter update

## Context

The values argument of UpdateProductFilter is nullable, and graphql-ruby
passes an explicitly-null argument through to the resolver as nil with
the key present.

## Description

Mapping nil to input hashes raised a NoMethodError, turning a malformed
payload into an internal error. A null values list now reaches the
validation layer and fails with value_is_mandatory like an empty one.

Author: rsempe

app/graphql/mutations/product_filters/update.rb

@@ -18,7 +18,7 @@ def resolve(**args)
         product_filter = current_organization.product_filters.find_by(id: args[:id])
 
         params = args.except(:id)
-        params[:values] = params[:values].map(&:to_h) if params.key?(:values)
+        params[:values] = params[:values]&.map(&:to_h) if params.key?(:values)
 
         result = ::ProductFilters::UpdateService.call(product_filter:, params:)
 

spec/graphql/mutations/product_filters/update_spec.rb

@@ -56,6 +56,14 @@
     expect(result_data["values"].map { [it["key"], it["value"]] }).to eq([%w[region eu]])
   end
 
+  context "when values is null" do
+    let(:input) { {id: product_filter.id, name: "After", values: nil} }
+
+    it "returns a validation error" do
+      expect_graphql_error(result: execution, message: :unprocessable_entity)
+    end
+  end
+
   context "when the filter belongs to another organization" do
     let(:input) { {id: create(:product_filter).id, name: "After"} }