class ActionController::Parameters

def [](key)

params[:none] # => nil
params[:person] # => #"Francesco"} permitted: false>
params = ActionController::Parameters.new(person: { name: "Francesco" })

returns +nil+.
Returns a parameter for the given +key+. If not found, 
def [](key)
  convert_hashes_to_parameters(key, @parameters[key])
end