Cannot copy current dir to container

[LijieZhou]

I am able to follow the tutorial until copying the current directory to /application directory in the image. I am not able to see the content get copied into the container somehow:

lijie@lijie-XPS-13-9350:~/rails-chat-tutorial$ ls
app  bin  config  config.ru  db  Dockerfile  Gemfile  Gemfile.lock  lib  LICENSE  log  package.json  public  Rakefile  README.md  storage  test  tmp  vendor
lijie@lijie-XPS-13-9350:~/rails-chat-tutorial$ cat Dockerfile 
FROM ruby:2.6.2-stretch
COPY . /application

lijie@lijie-XPS-13-9350:~/rails-chat-tutorial$ sudo docker run -i -t rails-chat-tutorial
irb(main):001:0> Dir['/application/*']
=> []
irb(main):002:0>