class ActionController::Parameters

def fetch(key, *args)

params.fetch(:none) { "Francesco" } # => "Francesco"
params.fetch(:none, "Francesco") # => "Francesco"
params.fetch(:none, {}) # => #
params.fetch(:none) # => ActionController::ParameterMissing: param is missing or the value is empty: none
params.fetch(:person) # => #"Francesco"} permitted: false>
params = ActionController::Parameters.new(person: { name: "Francesco" })

is given, then that will be run and its result returned.
instance of +ActionController::Parameters+ if possible); if a block
if a second argument is given, then that is returned (converted to an
it will raise an ActionController::ParameterMissing error;
can't be found, there are several options: With no other arguments,
Returns a parameter for the given +key+. If the +key+ 
def fetch(key, *args)
  convert_value_to_parameters(
    @parameters.fetch(key) {
      if block_given?
        yield
      else
        args.fetch(0) { raise ActionController::ParameterMissing.new(key, @parameters.keys) }
      end
    }
  )
end