it's a trivial thing though, i felt a little bit confused, if the argument is not a User instance, then how it become, 

```ruby
username = user
username = username # the actual
```

```ruby
def github_user_url(username)
  "https://github.com/#{ERB::Util.url_encode(username)}"
end
```

i'll do when this case... how do you think?