How to add polymorphic address to devise custom registration controller? - ruby-on-rails

Question

I'm trying to setup a custom registration controller using Devise and a polymorphic address model, but can't seem to actually get the address to save to the database.
Here is my controller:
class RegistrationsController < Devise::RegistrationsController
before_action :configure_permitted_parameters, if: :devise_controller?
def new
build_resource({})
resource.build_address
respond_with self.resource
end
def create
super
end
private
def configure_permitted_parameters
devise_parameter_sanitizer.permit(:sign_up) {|u|
u.permit(:first_name,:last_name,:mobile,:landline,:email,:password,:password_confirmation, :current_password, address_attributes: [:line_1,:line_2,:city,:region,:post_code,:country])
}
end
end
my user model:
class User < ApplicationRecord
devise :database_authenticatable, :registerable,:recoverable, :rememberable, :trackable, :validatable
has_one :address, through: :addressable
accepts_nested_attributes_for :address
... (other attributes)
my address model:
class Address < ApplicationRecord
belongs_to :addressable, polymorphic: true
end
relevant part of routes:
devise_for :users, :controllers => {registrations: 'registrations'}
devise_scope :user do
get '/login', to: 'devise/sessions#new'
get '/logout', to: 'devise/sessions#destroy'
get '/signup', to: 'devise/registrations#new'
end
and finally the relevant part of the view view:
<%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
<%= devise_error_messages! %>
<div class="field">
<%= f.label :first_name %><br/>
<%= f.text_field :first_name, autofocus: true %>
</div>
<div class="field">
<%= f.label :last_name %><br/>
<%= f.text_field :last_name, autofocus: true %>
</div>
<%= fields_for :address do |ff| %>
<div class="field">
<%= ff.label :line_1 %>
<%= ff.text_field :line_1 %>
</div>
<div class="field">
<%= ff.label :line_2 %>
<%= ff.text_field :line_2 %>
</div>
<div class="field">
<%= ff.label :city %>
<%= ff.text_field :city%>
</div>
<div class="field">
<%= ff.label :region%>
<%= ff.text_field :region%>
</div>
<div class="field">
<%= ff.label :post_code%>
<%= ff.text_field :post_code %>
</div>
<div class="field">
<%= ff.label :country %>
<%= ff.text_field :country%>
</div>
<% end %>
<div class="field">
<%= f.label :mobile %><br/>
<%= f.text_field :mobile, autofocus: true %>
</div>
<div class="field">
<%= f.label :landline %><br/>
<%= f.text_field :landline, autofocus: true %>
</div>
<div class="field">
<%= f.label :email %><br/>
<%= f.email_field :email, autofocus: true %>
</div>
<div class="field">
<%= f.label :password %>
<% if #minimum_password_length %>
<em>(<%= #minimum_password_length %> characters minimum)</em>
<% end %><br/>
<%= f.password_field :password, autocomplete: "off" %>
</div>
<div class="field">
<%= f.label :password_confirmation %><br/>
<%= f.password_field :password_confirmation, autocomplete: "off" %>
</div>
<div class="actions">
<%= f.submit "Sign up", class: "btn btn-default" %>
</div>
<% end %>
Any help would be much appreciated! :)