Nested one-to-one attribute does not save via form - ruby-on-rails

Question

I've got a form with a nested one-to-one attribute which I can't save into the dabase. I've been reading SO threads for four hours to try and solve it:
Contact.rb:
class Contact < ApplicationRecord
has_one :address
accepts_nested_attributes_for :address
end
Address.rb
class Address < ApplicationRecord
belongs_to :contact
end
Routes.rb
Rails.application.routes.draw do
resources :contacts do
resources :addresses
end
root :to => 'contacts#index'
end
The form
<%= form_for #contact do |f| %>
<div class="field">
<%= f.label :firstname %>
<%= f.text_field :firstname %>
</div>
<div class="field">
<%= f.label :lastname %>
<%= f.text_field :lastname %>
</div>
<%= f.fields_for :address do |address_fields| %>
<%= address_fields.label :streetname %>
<%= address_fields.text_field :streetname %>
<% end %>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
Controller:
class ContactsController < ApplicationController
before_action :find_contact, only: [:show, :edit, :update, :destroy]
def index
#contacts = Contact.all
end
def show
end
def new
#contact = Contact.new
#ontact.build_address
end
def create
#contact = Contact.new(contact_params)
if #contact.save
redirect_to #contact
else
render 'new'
end
end
(...)
private
def find_contact
#contact = Contact.find(params[:id])
end
def contact_params
params.require(:contact).permit(:firstname, :lastname,
address_attributes: [:contact_id, :streetname])
end
end
With the above code, nothing is saved and the transaction is rolled back. Earlier on, only the contact-details were saved whereas the address remained nil and the following line gave an error that "streetname" was unknown:
<p><%= #contact.address.streetname %></p>
Your help is much appreciated!

Answer 1

Thanks #fbelanger for leading me to the solution:
I noticed from the contents of "params" that permitted was set on false. I found via Google that Rails 5 requires the following addition in the address model, to the belongs_to line:
class Address < ApplicationRecord
belongs_to :contact, required: false
end
And now it's saved: hurray!