だって全部別にifでええやん。
irb(main):006:0* grades = { "Jane Doe" => 10, "Jim Doe" => 6 } => {"Jane Doe"=>10, "Jim Doe"=>6} irb(main):011:0> "Bingo!" unless grades.has_key?('Jim Doada') => "Bingo!" irb(main):015:0* "Bingo!" unless grades.has_key?('Jim Doe') => nil