Fix state=all 500 error bug (#4525) [ci skip]

app/services/article_api_index_service.rb

@@ -29,7 +29,7 @@ class ArticleApiIndexService
                  base_articles
                end
 
-    articles.decorate
+    articles&.decorate
   end
 
   private

spec/requests/api/v0/articles_spec.rb

@@ -15,6 +15,11 @@ RSpec.describe "Api::V0::Articles", type: :request do
         expect(response.content_type).to eq("application/json")
       end
 
+      it "returns nothing if params state=all is not found" do
+        get api_articles_path(state: "all")
+        expect(json_response.size).to eq(0)
+      end
+
       it "returns featured articles if no param is given" do
         article.update_column(:featured, true)
         get api_articles_path