FIX: Don't error out when loading a badge with a deleted image (#27688)

Badges can have their associated image uploads deleted. When this happens, any user who has that badge will have their profile page error out.

After this fix, when deleting an upload that's associated with a badge, we nullify the foreign key ID on the badge. This makes the existing safeguard work correctly.

app/models/upload.rb

@@ -27,6 +27,7 @@ class Upload < ActiveRecord::Base
   has_many :upload_references, dependent: :destroy
   has_many :posts, through: :upload_references, source: :target, source_type: "Post"
   has_many :topic_thumbnails
+  has_many :badges, foreign_key: :image_upload_id, dependent: :nullify
 
   attr_accessor :for_group_message
   attr_accessor :for_theme

spec/models/badge_spec.rb

@@ -98,15 +98,36 @@ RSpec.describe Badge do
   end
 
   describe "#image_url" do
-    it "has CDN url" do
+    before do
       SiteSetting.enable_s3_uploads = true
       SiteSetting.s3_cdn_url = "https://some-s3-cdn.amzn.com"
+    end
+
+    context "when the badge has an existing image" do
+      it "has a CDN url" do
         upload = Fabricate(:upload_s3)
         badge = Fabricate(:badge, image_upload_id: upload.id)
+
         expect(badge.image_url).to start_with("https://some-s3-cdn.amzn.com")
       end
     end
 
+    context "when the badge does not have a related image" do
+      it "does not have a CDN url" do
+        upload = Fabricate(:upload_s3)
+        badge = Fabricate(:badge, image_upload_id: upload.id)
+
+        store = stub
+        store.expects(:remove_upload).returns(true)
+        Discourse.stubs(:store).returns(store)
+
+        upload.destroy!
+
+        expect(badge.reload.image_url).to eq(nil)
+      end
+    end
+  end
+
   describe ".i18n_name" do
     it "transforms to lower case letters, and replaces spaces with underscores" do
       expect(Badge.i18n_name("Basic User")).to eq("basic_user")

spec/models/upload_spec.rb

@@ -16,6 +16,8 @@ RSpec.describe Upload do
   let(:attachment_path) { __FILE__ }
   let(:attachment) { File.new(attachment_path) }
 
+  it { is_expected.to have_many(:badges).dependent(:nullify) }
+
   describe ".with_no_non_post_relations" do
     it "does not find non-post related uploads" do
       post_upload = Fabricate(:upload)