```ruby
module Grabble
  class Vertex
    def initialize(data)
      @data = data
    end

    def data
      @data
    end

  end
end
```

Use attr_reader instead of manual getter method
user
```ruby
module Grabble
  class Vertex
    attr_reader :data

    def initialize(data)
      @data = data
    end
  end
end
```
assistant