Rails "TypeError (no implicit conversion of nil into String)" when loading images using image_tag, activeStorage and "has_many_attached"

Question

I am trying to follow this tutorial to upload multiple images for my model: https://www.youtube.com/watch?v=A23zCePXe74

The uploading and saving of the images into the database using activeStorage seems to work, but when I go to the show page the images are not rendered. I tried following these steps in a fresh rails app and the images showed up then, but when I try to follow the steps in an existing rails app, I get see a TypeError and Internal server error in my server console and the page loads without the images.

Any help or suggestion would be greatly appreciated.

My model looks like

class Post < ApplicationRecord
  has_many_attached :images
end

My controller looks like:

class PostsController < ApplicationController
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  config.relative_url_root = ""

  # GET /posts
  # GET /posts.json
  def index
    @posts = Post.all
  end

  # GET /posts/1
  # GET /posts/1.json
  def show
  end

  # GET /posts/new
  def new
    @post = Post.new
  end

  # GET /posts/1/edit
  def edit
  end

  # POST /posts
  # POST /posts.json
  def create
    @post = Post.new(post_params)

    respond_to do |format|
      if @post.save
        format.html { redirect_to @post, notice: 'Post was successfully created.' }
        format.json { render :show, status: :created, location: @post }
      else
        format.html { render :new }
        format.json { render json: @post.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /posts/1
  # PATCH/PUT /posts/1.json
  def update
    respond_to do |format|
      if @post.update(post_params)
        format.html { redirect_to @post, notice: 'Post was successfully updated.' }
        format.json { render :show, status: :ok, location: @post }
      else
        format.html { render :edit }
        format.json { render json: @post.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /posts/1
  # DELETE /posts/1.json
  def destroy
    @post.destroy
    respond_to do |format|
      format.html { redirect_to posts_url, notice: 'Post was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_post
      @post = Post.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def post_params
      params.require(:post).permit(:title, :body, images: [])
    end
end

My _form.html.erb looks like:

<%= form_with(model: post, local: true) do |form| %>
  <% if post.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(post.errors.count, "error") %> prohibited this post from being saved:</h2>

      <ul>
        <% post.errors.full_messages.each do |message| %>
          <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= form.label :title %>
    <%= form.text_field :title %>
  </div>

  <div class="field">
    <%= form.label :body %>
    <%= form.text_area :body %>
  </div>

    <div class="field">
      <%= form.label :images %>
        <%= form.file_field :images, multiple: true %>
    </div>

  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>

My show.html.erb looks like:

<p id="notice"><%= notice %></p>

<p>
  <strong>Title:</strong>
  <%= @post.title %>
</p>

<p>
  <strong>Body:</strong>
  <%= @post.body %>
</p>

<% (0...@post.images.count).each do |image| %>
  <%= image_tag(@post.images[image]) %>
<% end %>

<%= link_to 'Edit', edit_post_path(@post) %> |
<%= link_to 'Back', posts_path %>

My Gemfile looks like:

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '2.6.2'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 6.0.0.rc2'
# Use postgresql as the database for Active Record
gem 'pg', '>= 0.18', '< 2.0'
# Use Puma as the app server
gem 'puma', '~> 3.11'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5'
# Transpile app-like JavaScript. Read more: https://github.com/rails/webpacker
gem 'webpacker', '~> 4.0'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.7'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 4.0'
# Use Active Model has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use Active Storage variant
# gem 'image_processing', '~> 1.2'

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.4.2', require: false

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end

group :test do
  # Adds support for Capybara system testing and selenium driver
  gem 'capybara', '>= 2.15'
  gem 'selenium-webdriver'
  # Easy installation and use of web drivers to run system tests with browsers
  gem 'webdrivers'
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
gem 'redis'
gem 'braintree'
gem 'bcrypt'
gem 'foreman'
gem 'rails-controller-testing'
gem 'faker'
gem 'pagy'
gem 'figaro'
gem 'gon'
gem 'modernizr-rails'
gem 'stripe-rails'
gem 'paperclip'
# thirdparty authentications
gem 'omniauth-google-oauth2'
gem 'omniauth-facebook'
gem 'omniauth-twitter'
gem 'activerecord-session_store'
# for front end
gem 'react-rails'
gem 'bootstrap'
gem 'sprockets-rails'
gem 'jquery-rails'
# catches test emails
gem 'mailcatcher'
gem 'devise'
# admin panel
gem 'rails_admin'

# active storage variant
gem 'mini_magick', '~> 4.8'

The error I see in my server console is:

  Parameters: {"content_type"=>"image/jpeg", "disposition"=>"inline; filename=\"Capture.JPG\"; filename*=UTF-8''Capture.JPG", "encoded_key"=>"eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaDdDRG9JYTJWNVNTSWhaamM1YlRGNmFtdDNNM0p0ZFhwaE5UTnljekYxWW1kaWFIbHFaUVk2QmtWVU9oQmthWE53YjNOcGRHbHZia2tpUVdsdWJHbHVaVHNnWm1sc1pXNWhiV1U5SWtOaGNIUjFjbVV1U2xCSElqc2dabWxzWlc1aGJXVXFQVlZVUmkwNEp5ZERZWEIwZFhKbExrcFFSd1k3QmxRNkVXTnZiblJsYm5SZmRIbHdaVWtpRDJsdFlXZGxMMnB3WldjR093WlUiLCJleHAiOiIyMDIwLTAxLTExVDA0OjA2OjUwLjc2MFoiLCJwdXIiOiJibG9iX2tleSJ9fQ==--983c22b711b8ba21f15b0f7ce768a3165fe9810a", "filename"=>"Capture"}

TypeError (no implicit conversion of nil into String):

rack (2.1.0) lib/rack/files.rb:25:in `expand_path'
rack (2.1.0) lib/rack/files.rb:25:in `initialize'
activestorage (6.0.2.1) app/controllers/active_storage/disk_controller.rb:45:in `new'
activestorage (6.0.2.1) app/controllers/active_storage/disk_controller.rb:45:in `serve_file'
activestorage (6.0.2.1) app/controllers/active_storage/disk_controller.rb:12:in `show'
actionpack (6.0.2.1) lib/action_controller/metal/basic_implicit_render.rb:6:in `send_action'
actionpack (6.0.2.1) lib/abstract_controller/base.rb:196:in `process_action'
actionpack (6.0.2.1) lib/action_controller/metal/rendering.rb:30:in `process_action'
actionpack (6.0.2.1) lib/abstract_controller/callbacks.rb:42:in `block in process_action'
.
.
.
puma (3.12.2) lib/puma/configuration.rb:227:in `call'
puma (3.12.2) lib/puma/server.rb:674:in `handle_request'
puma (3.12.2) lib/puma/server.rb:476:in `process_client'
puma (3.12.2) lib/puma/server.rb:334:in `block in run'
puma (3.12.2) lib/puma/thread_pool.rb:135:in `block in spawn_thread'
Completed 500 Internal Server Error in 1ms (ActiveRecord: 0.0ms | Allocations: 623)

Another strange thing I see whenever I run "rails db" is:

Rack::File is deprecated, please use Rack::Files instead.
psql (12.1 (Ubuntu 12.1-1.pgdg18.04+1), server 11.5 (Ubuntu 11.5-1.pgdg18.04+1))
Type "help" for help.

Answer 1

I updated my 'rack' gem to 2.2.2 to fix this issue using bundle update rack. The way I found out this solution was navigating to the issue opened by @guillaume and they had corrected the issue with the newer 'rack' version.

Answer 2

I just stumbled upon this one too.

TL;DR use gem 'rack', '~> 2.0.8' in your Gemfile

It seems last version of rack uses expand_path on the root here: https://github.com/rack/rack/commit/8f85307711ca5e7a4729641fda1552890ffa129a#diff-894804c816a11584eb28499cb8bbe396R25

It seems that version 6.2.0.1 of Rails uses Rack::File.new(nil) here: https://github.com/rails/rails/commit/feab7031b57040afa2b2f5f78f9251dbad6cbdf8#diff-17640e7129bc730594120c1ac91d7928L45

In newer version of Rails (in Github at the moment only), it doesn't break because it has been changed. But in the current version, it does break.

You can downgrade rack to version 2.0.8 with gem 'rack', '~> 2.0.8' at the moment.

EDIT: I opened an issue on Rack here: https://github.com/rack/rack/issues/1471