Fix NoMethodError on Nil for article preview (#16569)

* Fix NoMethodError on Nil for article preview

* Remove commented out debugging code

app/controllers/articles_controller.rb

@@ -90,11 +90,19 @@ class ArticlesController < ApplicationController
         format.json { render json: @article.errors, status: :unprocessable_entity }
       else
         format.json do
+          front_matter = parsed.front_matter.to_h
+          if front_matter["tags"]
+            tags = Article.new.tag_list.add(front_matter["tags"], parser: ActsAsTaggableOn::TagParser)
+          end
+          if front_matter["cover_image"]
+            cover_image = ApplicationController.helpers.cloud_cover_url(front_matter["cover_image"])
+          end
+
           render json: {
             processed_html: processed_html,
-            title: parsed["title"],
-            tags: (Article.new.tag_list.add(parsed["tags"], parser: ActsAsTaggableOn::TagParser) if parsed["tags"]),
-            cover_image: (ApplicationController.helpers.cloud_cover_url(parsed["cover_image"]) if parsed["cover_image"])
+            title: front_matter["title"],
+            tags: tags,
+            cover_image: cover_image
           }, status: :ok
         end
       end

spec/requests/editor_spec.rb

@@ -66,5 +66,24 @@ RSpec.describe "Editor", type: :request do
         expect(response.media_type).to eq("application/json")
       end
     end
+
+    context "with front matter" do
+      it "returns successfully" do
+        sign_in user
+        article_body = <<~MARKDOWN
+          ---
+          ---
+
+          Hello
+        MARKDOWN
+
+        post "/articles/preview",
+             headers: headers,
+             params: { article_body: article_body },
+             as: :json
+
+        expect(response).to be_successful
+      end
+    end
   end
 end