何も入力せずにenterした場合、ここで `NoMethodError` があがっちゃうので、105 行目のチェックをこの手前でやるようにした方がよさそうです :snake:
```
battleship.rb:102:in `target': undefined method `upcase' for nil:NilClass (NoMethodError)
	from battleship.rb:98:in `hit'
	from battleship.rb:83:in `block in judge'
	from battleship.rb:82:in `each'
	from battleship.rb:82:in `judge'
	from battleship.rb:131:in `<main>'
```