Allow overriding serializer key with empty value

[floriandejonckheere]

Allow specifying an empty key in the controller, overriding a key set (or automatically generated) in the serializer class.

class PersonSerializer < CacheCrispies::Base
  key :person

  serialize :name
end

cache_render Person.new(name: "John Doe")
# => { person: { name: "John Doe" } }

cache_render Person.new(name: "John Doe"), key: nil
# => { name: "John Doe" }

[adamcrown]

Makes sense. Thanks for the PR!

[adamcrown]

I just released version 1.4.0. Thanks again!