前提・実現したいこと

※cloud9を開発環境としてつかっています。

現在簡単な投稿のアプリをRailsで作っているのですが、
すでに投稿されたものを修正する機能を追加しようとしたときに
編集をすると
undefined method `update' for nil:NilClass
というエラーが出てしまい、編集が完了できません。

発生している問題・エラーメッセージ

画像の説明をここに入力

undefined method `update' for nil:NilClass

追記：
id:12のデータを投稿後に編集するようにしたいので
コメントいただいたようにデータが入っていないのかな？と見たところ

2.6.0 :004 > Article.find(12)
  Article Load (0.2ms)  SELECT  "articles".* FROM "articles" WHERE "articles"."id" = ? LIMIT ?  [["id", 12], ["LIMIT", 1]]
 => #<Article id: 12, title: "testing article", description: "this is a test", created_at: "2019-06-21 19:13:10", updated_at: "2019-06-21 19:13:10"> 
2.6.0 :005 >

となっており、データ自体は存在するようです。

development.logのエラーが出ているところのログです。

app/controllers/articles_controller.rb:23:in `update'
  [1m[36mArticle Load (0.4ms)[0m  [1m[34mSELECT  "articles".* FROM "articles" LIMIT ?[0m  [["LIMIT", 11]]
  [1m[36mArticle Load (0.2ms)[0m  [1m[34mSELECT  "articles".* FROM "articles" WHERE "articles"."id" = ? LIMIT ?[0m  [["id", 12], ["LIMIT", 1]]
Started GET "/articles/12/edit" for 39.111.211.9 at 2019-06-22 05:22:48 +0000
Cannot render console from 39.111.211.9! Allowed networks: 127.0.0.1, ::1, 127.0.0.0/127.255.255.255
  [1m[35m (0.1ms)[0m  [1m[34mSELECT "schema_migrations"."version" FROM "schema_migrations" ORDER BY "schema_migrations"."version" ASC[0m
  ↳ /home/ec2-user/.rvm/gems/ruby-2.6.0/gems/activerecord-5.2.3/lib/active_record/log_subscriber.rb:98
Processing by ArticlesController#edit as HTML
  Parameters: {"id"=>"12"}
  [1m[36mArticle Load (0.1ms)[0m  [1m[34mSELECT  "articles".* FROM "articles" WHERE "articles"."id" = ? LIMIT ?[0m  [["id", 12], ["LIMIT", 1]]
  ↳ app/controllers/articles_controller.rb:7
  Rendering articles/edit.html.erb within layouts/application
  Rendered articles/edit.html.erb within layouts/application (4.7ms)
Completed 200 OK in 215ms (Views: 200.8ms | ActiveRecord: 0.7ms)


Started PATCH "/articles/12" for 39.111.211.9 at 2019-06-22 05:22:56 +0000
Cannot render console from 39.111.211.9! Allowed networks: 127.0.0.1, ::1, 127.0.0.0/127.255.255.255
Processing by ArticlesController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"RvxoB0HoLqxeKxzzVF0q3RnSwQ2Gt6NQGXQ2v3JArvL0SmVMx95vddWBXKBndq0nKbBE7W8lp+M5ryxJIZvWLg==", "article"=>{"title"=>"testing article", "description"=>"this is a test edited"}, "commit"=>"Update Article", "id"=>"12"}
  [1m[36mArticle Load (0.1ms)[0m  [1m[34mSELECT  "articles".* FROM "articles" WHERE "articles"."id" = ? LIMIT ?[0m  [["id", 12], ["LIMIT", 1]]
  ↳ app/controllers/articles_controller.rb:22
Completed 500 Internal Server Error in 2ms (ActiveRecord: 0.1ms)

該当のソースコード

github:
https://github.com/yuks0810/alpha-blog

class ArticlesController < ApplicationController
  def new 
    @article = Article.new
  end

  def edit
    @article = Article.find(params[:id])
  end

  def create
    @article = Article.new(article_params)
    if @article.save
      flash[:notice] = "Article was successfully created"
      redirect_to article_path(@article)
    else
      render 'new'
    end
  end
  # create action does not need a template as def new does

  def update 
    @artcle = Article.find(params[:id])
    if @article.update(article_params)
        flash[:notice] = "Article was successfully updated"
        redirect_to article_path(@article)
    else
      render "edit"
    end
  end

  def show 
    @article = Article.find(params[:id])
  end

  private
    def article_params
      params.require(:article).permit(:title, :description)
    end

end

undefined methodとなっていますが、def updateで定義していてタイポでもないと思うので
なぜエラーが出るのかわかりません。

どなたかわかる方いらっしゃいましたらご教示お願い致します。