Cannot remove all variants from a product

app/models/spree/product_decorator.rb

@@ -23,6 +23,7 @@ Spree::Product.class_eval do
 
   before_validation :ensure_standard_variant, if: :new_record?
 
+  validates_presence_of :variants, message: "Product must have at least one variant"
   validates_presence_of :supplier
   validates :primary_taxon, presence: { message: "^Product Category can't be blank" }
   validates :tax_category_id, presence: { message: "^Tax Category can't be blank" }, if: "Spree::Config.products_require_tax_category"

spec/models/spree/product_spec.rb

@@ -8,7 +8,7 @@ module Spree
       it { should belong_to(:primary_taxon) }
       it { should have_many(:product_distributions) }
     end
-    
+
     describe "validations and defaults" do
       it "is valid when built from factory" do
         build(:product).should be_valid
@@ -61,6 +61,14 @@ module Spree
       end
 
 
+      it "does not allow only standard variant to be deleted" do
+        product = create(:simple_product)
+        expect(product.variants(:reload).length).to eq 1
+        product.variants = []
+        expect(product.save).to be_false
+        expect(product.errors[:variants]).to include "Product must have at least one variant"
+      end
+
       context "when the product has variants" do
         let(:product) do
           product = create(:simple_product)