Validate that global new URL is absent if the global type is "archive"

Currently, there is validation in place to prevent the creation of sites which
have a global type of "redirect" without a global new URL, but the opposite
validation is missing.

app/models/site.rb

@@ -25,6 +25,7 @@ class Site < ApplicationRecord
   validates :abbr, uniqueness: true, presence: true, format: { with: /\A[a-zA-Z0-9_-]+\z/, message: "can only contain alphanumeric characters, underscores and dashes" }
   validates :special_redirect_strategy, inclusion: { in: SPECIAL_REDIRECT_STRATEGY_TYPES, allow_nil: true }
   validates :global_new_url, presence: { if: :global_redirect? }
+  validates :global_new_url, absence: { if: :global_archive? }
   validates :global_new_url,
             format: { without: /\?/,
                       message: "cannot contain a query when the path is appended",

spec/models/site_spec.rb

@@ -41,6 +41,15 @@
       end
     end
 
+    context "global archive" do
+      subject(:site) { build(:site, global_type: "archive", global_new_url: "http://a.com/") }
+
+      before { expect(site).not_to be_valid }
+      it "should validate absence of global_new_url" do
+        expect(site.errors[:global_new_url]).to eq(["must be blank"])
+      end
+    end
+
     context "global redirect with path appended" do
       subject(:site) { build(:site, global_type: "redirect", global_redirect_append_path: true, global_new_url: "http://a.com/?") }