Make enterprise mandatory for a voucher

It should have already been the case...

app/models/voucher.rb

@@ -3,7 +3,7 @@
 class Voucher < ApplicationRecord
   acts_as_paranoid
 
-  belongs_to :enterprise
+  belongs_to :enterprise, optional: false
 
   has_many :adjustments,
            as: :originator,

spec/models/spree/order_spec.rb

@@ -1432,6 +1432,8 @@ describe Spree::Order do
   end
 
   describe "#voucher_adjustments" do
+    let(:distributor) { create(:distributor_enterprise) }
+    let(:order) { create(:order, user: user, distributor: distributor) }
     let(:voucher) { create(:voucher, code: 'new_code', enterprise: order.distributor) }
 
     context "when no voucher adjustment" do
@@ -1441,7 +1443,6 @@ describe Spree::Order do
     end
 
     it "returns an array of voucher adjusment" do
-      order.save!
       expected_adjustments = Array.new(2) { voucher.create_adjustment(voucher.code, order) }
 
       expect(order.voucher_adjustments).to eq(expected_adjustments)

spec/models/voucher_spec.rb

@@ -6,7 +6,7 @@ describe Voucher do
   let(:enterprise) { build(:enterprise) }
 
   describe 'associations' do
-    it { is_expected.to belong_to(:enterprise) }
+    it { is_expected.to belong_to(:enterprise).required }
     it { is_expected.to have_many(:adjustments) }
   end