Sidebar and rendering partial, trying to run a todo app on sidebar - ruby-on-rails

Question

I am new to ruby on rails, I have been recommended to using a sidebar so that on most pages it will show what I want. I currently have an application on its own page called Todo List. It simply let you create a task and displays the tasks. It runs on its own page. Now I want to move that app and let it function in my sidebar. I have implemented my sidebar as follow.
/views/layouts/application (in body)
<%= yield :sidebar %>
/views/myapp1/index
<% content_for(:sidebar) do %>
<% render :partial => "layouts/sidebar" %>
<% end %>
/views/layouts/_sidebar
<% if logged_in? %>
<div id="mySidenav" class="sidenav">
<div class="row", id="container_todo_lists">
<%= render #todo_lists %>
</div>
<div class="links" data-toggle="modal" data-target="#mynewtodo_list">
<%= link_to('New Todo List', 'javascript:;', :id => :random) %>
</div>
×
</div>
<span style="font-size:30px;cursor:pointer" onclick="openNav()">☰ Todo List</span>
<script>
function openNav() {document.getElementById("mySidenav").style.width = "250px";}
function closeNav() {document.getElementById("mySidenav").style.width = "0";}
</script>
<% end %>
<!-- Modal create action -->
<%= form_for(#todo_list, remote: true) do |f| %>
<div class="modal fade" id="mynewtodo_list" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">×</span></button>
<h4 class="modal-title" id="myModalLabel">Todo</h4>
</div>
<div class="modal-body">
<div class="field">
<%= f.label :title %><br>
<%= f.text_area :title, class: "form-control todo_list_title" %>
</div>
<div class="field">
<%= f.label :description %><br>
<%= f.text_area :description, class: "form-control todo_list_content" %>
</div>
</div>
<div class="modal-footer">
<%= submit_tag "Create", class: "btn btn-primary" %>
<button type="button" class="btn btn-default" data-dismiss="modal" id="mynewtodo_listclose">Close</button>
</div>
</div>
</div>
</div>
<% end %>
<!-- Modal -->
I get this error
'nil' is not an ActiveModel-compatible object. It must implement :to_partial_path.
I think I know part of the problem is my
#todo_lists
Because I tried to called the sidebar on my todo_list page and it works, but the sidebar messed up my original application so that when I press edit and show it would turn the screen grey. Any suggestion is greatly appreciated. Thanks in advance.
/views/todo_lists/_todo_list.html.erb
<div class="text-center" id="todo_list_<%= todo_list.id %>">
<h3 class="panel-title"><%= todo_list.title %>
<sup style="color: #3BB2D6; position: absolute; top: 5px; right: 15px; text-align:right;">
(<%= time_ago_in_words(todo_list.created_at) %>)
</sup>
</h3>
<p><%= todo_list.description %></p>
<div class="row" role="group">
<div class="links1" data-toggle="modal" data-target="#myupdatetodo_list_<%= todo_list.id %>">
<%= link_to('Edit', 'javascript:;', :id => :random) %>
</div>
<div class="links1" data-toggle="modal" data-target="#myitemtodo_list_<%= todo_list.id %>">
<%= link_to('Show', 'javascript:;', :id => :random) %>
</div>
<div class="links1">
<%= link_to 'Destroy', todo_list, method: :delete, remote: true %>
</div>
</div>
<!-- Modal - update posts -->
<%= form_for(todo_list, :method => :put, remote: true) do |f| %>
<div class="modal fade" id="myupdatetodo_list_<%= todo_list.id %>" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">×</span></button>
<h4 class="modal-title" id="myModalLabel">Edit</h4>
</div>
<div class="modal-body">
<div class="field">
<%= f.label :title %><br>
<%= f.text_area :title, class: "form-control" %>
</div>
<div class="field">
<%= f.label :description %><br>
<%= f.text_area :description, class: "form-control" %>
</div>
</div>
<div class="modal-footer">
<button type="button" id="myupdatebutton_<%= todo_list.id %>" class="btn btn-default" data-dismiss="modal">Close</button>
<%= submit_tag "Update", class: "btn btn-primary" %>
</div>
</div>
</div>
</div>
<% end %>
<!-- Modal -->
<!-- Modal - item posts -->
<%= form_for(todo_list, :method => :put, remote: true) do |f| %>
<div class="modal fade" id="myitemtodo_list_<%= todo_list.id %>" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">×</span></button>
<h4 class="modal-title" id="myModalLabel">Items</h4>
</div>
<div class="modal-body">
<h3><%= todo_list.title %></h3>
<p><%= todo_list.description %></p>
</div>
<div class="modal-footer">
<button type="button" id="myitembutton_<%= todo_list.id %>" class="btn btn-default" data-dismiss="modal">Close</button>
<%= submit_tag "Add Item", class: "btn btn-primary" %>
</div>
</div>
</div>
</div>
<% end %>
<!-- Modal -->

Answer 1

In your case, that is because the #todo_lists isn't being set, I'm sure if you go back to the previous url that was rendering the view, the sidebar would show.
A way to resolve is to ensure it's set on every page as such:
class ApplicationController
before_action :set_to_do_lists
def set_to_do_lists
#todo_lists ||= TodoList.all #assign this to what's in your todo_lists_path
end
end
With that I guess your app should be fixed