undefined method `model_name' for NilClass:Class _MHartl - ruby-on-rails

Question

Quick overview: Clicked on my 'Settings' tab on my app and the following error came up. Haven't seen this one before, hope we can solve it with your help.
Error MSG Below + Log:
NoMethodError in Users#edit
Showing /Users/users/Sites/rails_projects/sample_app1/app/views/users/edit.html.erb where line #2 raised:
undefined method `model_name' for NilClass:Class
Extracted source (around line #2):
1: <h1>Edit user</h1>
2: <%= form_for(#user) do |f| %>
3: <%= render 'fields', :f => f %>
4: <br />
5: <div class="actions">
Full trace:
activemodel (3.2.11) lib/active_model/naming.rb:163:in `model_name_from_record_or_class'
activemodel (3.2.11) lib/active_model/naming.rb:158:in `param_key'
actionpack (3.2.11) lib/action_view/helpers/form_helper.rb:369:in `form_for'
app/views/users/edit.html.erb:2:in `_app_views_users_edit_html_erb__3405427518964834174_70263460873980'
actionpack (3.2.11) lib/action_view/template.rb:145:in `block in render'
activesupport (3.2.11) lib/active_support/notifications.rb:125:in `instrument'
actionpack (3.2.11) lib/action_view/template.rb:143:in `render'
actionpack (3.2.11) lib/action_view/renderer/template_renderer.rb:47:in `block (2 levels) in render_template'
actionpack (3.2.11) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (3.2.11) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.11) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.11) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.11) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (3.2.11) lib/action_view/renderer/template_renderer.rb:46:in `block in render_template'
actionpack (3.2.11) lib/action_view/renderer/template_renderer.rb:54:in `render_with_layout'
actionpack (3.2.11) lib/action_view/renderer/template_renderer.rb:45:in `render_template'
actionpack (3.2.11) lib/action_view/renderer/template_renderer.rb:18:in `render'
actionpack (3.2.11) lib/action_view/renderer/renderer.rb:36:in `render_template'
actionpack (3.2.11) lib/action_view/renderer/renderer.rb:17:in `render'
actionpack (3.2.11) lib/abstract_controller/rendering.rb:110:in `_render_template'
actionpack (3.2.11) lib/action_controller/metal/streaming.rb:225:in `_render_template'
actionpack (3.2.11) lib/abstract_controller/rendering.rb:103:in `render_to_body'
actionpack (3.2.11) lib/action_controller/metal/renderers.rb:28:in `render_to_body'
actionpack (3.2.11) lib/action_controller/metal/compatibility.rb:50:in `render_to_body'
actionpack (3.2.11) lib/abstract_controller/rendering.rb:88:in `render'
actionpack (3.2.11) lib/action_controller/metal/rendering.rb:16:in `render'
actionpack (3.2.11) lib/action_controller/metal/instrumentation.rb:40:in `block (2 levels) in render'
activesupport (3.2.11) lib/active_support/core_ext/benchmark.rb:5:in `block in ms'
/usr/local/rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/benchmark.rb:295:in `realtime'
activesupport (3.2.11) lib/active_support/core_ext/benchmark.rb:5:in `ms'
actionpack (3.2.11) lib/action_controller/metal/instrumentation.rb:40:in `block in render'
actionpack (3.2.11) lib/action_controller/metal/instrumentation.rb:83:in `cleanup_view_runtime'
activerecord (3.2.11) lib/active_record/railties/controller_runtime.rb:24:in `cleanup_view_runtime'
actionpack (3.2.11) lib/action_controller/metal/instrumentation.rb:39:in `render'
actionpack (3.2.11) lib/action_controller/metal/implicit_render.rb:10:in `default_render'
actionpack (3.2.11) lib/action_controller/metal/implicit_render.rb:5:in `send_action'
actionpack (3.2.11) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.11) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.11) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.11) lib/active_support/callbacks.rb:436:in `_run__1973298596514767122__process_action__4589837863867957684__callbacks'
activesupport (3.2.11) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.11) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.11) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.11) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.11) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.11) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.11) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.11) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.11) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.11) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.11) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
activerecord (3.2.11) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.11) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.11) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.11) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.11) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.11) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.11) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.11) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.11) lib/action_dispatch/routing/route_set.rb:36:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `block in call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.11) lib/action_dispatch/routing/route_set.rb:601:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.5) lib/rack/etag.rb:23:in `call'
rack (1.4.5) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.5) lib/rack/session/abstract/id.rb:210:in `context'
rack (1.4.5) lib/rack/session/abstract/id.rb:205:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/cookies.rb:341:in `call'
activerecord (3.2.11) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.11) lib/active_support/callbacks.rb:405:in `_run__3212209880191913765__call__3512108980805379927__callbacks'
activesupport (3.2.11) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.11) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.11) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.11) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.11) lib/rails/rack/logger.rb:32:in `call_app'
railties (3.2.11) lib/rails/rack/logger.rb:16:in `block in call'
activesupport (3.2.11) lib/active_support/tagged_logging.rb:22:in `tagged'
railties (3.2.11) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.5) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.5) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.11) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.5) lib/rack/lock.rb:15:in `call'
actionpack (3.2.11) lib/action_dispatch/middleware/static.rb:62:in `call'
railties (3.2.11) lib/rails/engine.rb:479:in `call'
railties (3.2.11) lib/rails/application.rb:223:in `call'
rack (1.4.5) lib/rack/content_length.rb:14:in `call'
railties (3.2.11) lib/rails/rack/log_tailer.rb:17:in `call'
rack (1.4.5) lib/rack/handler/webrick.rb:59:in `service'
/usr/local/rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
/usr/local/rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
/usr/local/rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'
_edit.html.erb file:
<h1>Edit user</h1>
<%= form_for(#user) do |f| %>
<%= render 'fields', :f => f %>
<br />
<div class="actions">
<%= f.submit "Update" %>
</div>
<% end %>
<br />
<div>
<%= gravatar_for #user %>
<a href="http://gravatar.com/emails" target=_blank>Change</a>
</div>
// Edit added - Users controller:
class UsersController < ApplicationController
before_filter :authenticate, :only => [:index, :edit, :update, :destroy]
before_filter :current_user, :only => [:edit, :update]
before_filter :admin_user, :only => :destroy
def index
#users = User.paginate(:page => params[:page])
#title = "All users"
end
def show
#user = User.find(params[:id])
#title = #user.name
end
def new
#user = User.new
#title = "Sign up"
end
def create
#user = User.new(params[:user])
if #user.save
sign_in #user
redirect_to #user, :flash => {:success => "Welcome"}
else
#title = "Sign up"
render 'new'
end
end
def edit
#title = "Edit use"
end
def update
if #user.update_attributes(params[:user])
redirect_to #user, :flash => {:success => "Profile updated." }
else
#title = "Edit use"
render 'edit'
end
end
def destroy
User.find(params[:id]).destroy
redirect_to users_path, :flash => { :success => "User destroyed." }
end
private
def authenticate
deny_access unless signed_in?
end
def correct_user
#user = User.find(params[:id])
redirect_to(root_path) unless current_user?(#user)
end
def admin_user
user = User.find(params[:id])
redirect_to(root_path) if !current_user.admin? || current_user?(user)
end
end

Answer 1

your edit action in UsersController should be smth like:
def edit
#user = User.find(params[:id])
#title = "Edit use"
end

Answer 2

Looks like you are missing an action for '/users/edit' and therefore #user is nil.
Add something like this to your controller.
def edit
#user = User.find(params[:id])
respond_with(#user) do |format|
format.html
end
end