Passing the NullSerializer downstream to the Message{Encryptor,Verifier} allows us to handle the (de)serialization step within the cookie jar, which gives us the opportunity to detect and migrate legacy cookies.

Methods
D
L
Class Public methods
dump(value)

Source: show | on GitHub 

# File actionpack/lib/action_dispatch/middleware/cookies.rb, line 404
def self.dump(value)
  value
end
load(value)

Source: show | on GitHub 

# File actionpack/lib/action_dispatch/middleware/cookies.rb, line 400
def self.load(value)
  value
end