新規会員登録をウィザード形式で作成

#解決したいこと
新規会員登録をウィザード形式で作成しています。会員情報(user)→住所(sending_destination)の順にページを移動して入力します。
会員登録にはdeviseを使用。ページ移動時には入力情報をsessionに保持します。
会員情報を入力後、住所入力ページに移動する際に以下のエラーが発生しています。

#エラー内容

new_sending_destination.html.haml

.main-form
      = form_for @sending_destination do |f|
        = devise_error_messages!
        %h2.main-form__title お届け先住所入力
        .main-form__wrapper
          .main-contents
            .contents-field
              = f.label :お名前（全角）   
              %span.contents-field__require 必須
              = f.text_field :family_name, class:"contents-field__input half", placeholder:"例）山田"
              = f.text_field :first_name, class:"contents-field__input half", placeholder:"例）太郎"
            .contents-field
              = f.label :お名前カナ（全角）
              %span.contents-field__require 必須
              = f.text_field :family_name_kana, class:"contents-field__input half", placeholder:"例）ヤマダ"
              = f.text_field :first_name_kana, class:"contents-field__input half", placeholder:"例）タロウ"
            .contents-field
              = f.label :郵便番号
              %span.contents-field__require 必須
              = f.number_field :post_code, class:"contents-field__input", placeholder:"例）555-7777"
            .contents-field
              = f.label :都道府県
              %span.contents-field__require 必須
              = f.text_field :prefecture_code, class:"contents-field__input", placeholder:"例）555-7777"
            .contents-field
              = f.label :市区町村
              %span.contents-field__require 必須
              = f.text_field :city, class:"contents-field__input", placeholder:"例）渋谷区"
            .contents-field
              = f.label :番地
              %span.contents-field__require 必須
              = f.text_field :house_number, class:"contents-field__input", placeholder:"例）神南１丁目１８−２"
            .contents-field
              = f.label :番地
              %span.contents-field__require 任意
              = f.text_field :building_name, class:"contents-field__input", placeholder:"例）フレーム神南坂 4階"
            .contents-field
              = f.label :電話番号
              %span.contents-field__require 任意
              = f.number_field :phone_number, class:"contents-field__input", placeholder:"例）22233334444"

sending_destination.rb

class SendingDestination < ApplicationRecord
  belongs_to :user, optional: true
  validates :post_code, :prefecture_code, :city, :house_number, :building_name, :phone_number ,presence: true
end

registration_controller.rb

class Users::RegistrationsController < Devise::RegistrationsController
  before_action :configure_sign_up_params, only: [:create]

  def new
    @user = User.new
  end

  def create
    @user = User.new(sign_up_params)
    unless @user.valid?
      flash.now[:alert] = @user.errors.full_messages
      render :new and return
    end
    session["devise.regist_data"] = {user: @user.attributes}
    session["devise.regist_data"][:user]["password"] = params[:user][:password]
    @sending_destination = @user.sending_destination
    render :new_sending_destination
  end

  def create_sending_destination
    @user = User.new(session["devise.regist_data"]["user"])
    @sending_destination = SendingDestination.new(sending_destination_params)
    unless @sending_destination.valid?
      flash.now[:alert] = @sending_destination.errors.full_messages
      render :new_sending_destination and return
    end
    @user.build_sending_destination(@sending_destination.attributes)
    @user.save
    sign_in(:user, @user)
  end

  protected
  def configure_sign_up_params
    devise_parameter_sanitizer.permit(:sign_up, keys: [:attribute])
  end

  def sending_destination_params
    params.require(:sending_destination).permit(:post_code, :prefecture_code, :city, :house_number, :building_name, :phone_number)
  end

maigation(sending_desitnation)

class CreateSendingDestinations < ActiveRecord::Migration[5.0]
  def change
    create_table :sending_destinations do |t|
      t.string  :destination_family_name, null: false
      t.string  :destination_first_name, null: false
      t.string  :destination_first_name_kana, null: false
      t.string  :destination_family_name_kana, null: false
      t.integer :post_code, null: false
      t.integer :prefecture_code, null: false
      t.string  :city, null:false
      t.string  :house_number, null: false
      t.string  :building_name
      t.integer :phone_number, unique: true
      t.references :user, foreign_key: true
    end
  end
end

よろしくお願いいたします。