「Ruby初心者」　投稿したデータの一覧が表示できなくて困っております。

<% require 'active_support/core_ext/numeric/conversions' %>
<h2>収入科目の新規データ登録</h2>
<p>登録年月を設定してください</p>
<%= form_tag({controller: :income_values, action: :new}, {method: :post}) do %>
    <input type="month" name="year_month">
    <input type="submit">
<% end %>

<h2>収入科目 データ一覧 </h2>
<% if @income_value.present? %>
<table>
  <tr>
    <th>登録年月</th>
    <th>名称</th>
    <th>値</th>
    <th>備考</th>
    <th>操作</th>
  </tr>
    <% @income_values.each do |income_value| %>
  <tr>
        <td><%= income_value.year_month.strftime('%Y年%m月') %></td>
        <td><%= @incomes.find(income_value.income_id).name %></td>
        <td><%= income_value.value.to_s(:delimited) %> 円</td>
        <td><%= income_value.description %></td>
        <td><%= link_to "編集", [:edit, income_value] %> | <%= link_to "削除", income_value, method: :delete, data: { confirm: "本当に削除しますか？"} %></td>
  </tr>
  <% end %>
</table>
<% else %>
    <p>登録されているデータがありません。</p>
<% end %>

class IncomeValuesController < ApplicationController

    def index
      @incomes = Income.order(created_at: :asc)
        @income_values = IncomeValue.order("year_month asc")
    end

    def show
        @income_value = IncomeValue.find(params[:id])
    end

    def new
        year_month_day = params[:year_month] + "-01"
        @year_month = year_month_day.to_date

        @incomes = Income.order(created_at: :asc)
        @form = Form::IncomeForm.new
    end

    def edit
        @income_value = IncomeValue.find(params[:id])
        @income = Income.find(@income_value.income_id)
    end

    def create
        @form = Form::IncomeForm.new(income_form_params)
        if @form.save
            redirect_to :income_values, notice: "登録しました"
        else
            redirect_to :income_values, notice: "登録に失敗しました"
        end
    end

    def income_form_params
        params
            .require(:form_income_form)
            .permit(income_values_attributes: Form::IncomeValue::REGISTRABLE_ATTRIBUTES)
    end

    def update
        @income_value = IncomeValue.find(params[:id])
        @income_value.assign_attributes(params[:income_value])
        if @income_value.save
            redirect_to :income_values, notice: "情報を更新しました"
        else