undefined method `model_name' for NilClass:Class, new action - ruby-on-rails

Question

I've been trying to edit the default scaffolding, and have been thus far quite successful. However, this little puzzle has managed to boggle me, as even reverting the file to it's original state isn't working. It's throwing up a "undefined method `model_name' for NilClass:Class" as the title suggests.
New Action In User Controller:
def new
if #current_user
redirect_to(action: 'home')
else
#user = User.new
end
respond_to do |format|
format.html # new.html.erb
format.json { render json: #user }
end
end
_form.html.erb beginning
<%= form_for(#user) do |f| %>
<% if #user.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#user.errors.count, "error") %> prohibited this user from being saved:</h2>
<ul>
<% #user.errors.full_messages.each do |msg| %>
Any help would be appreciated!

Answer 1

In the case when #current_user is set, your new action doesn't stop executing after the redirect_to. Execution proceeds to the respond_to block, which attempts to render the page without setting #user, resulting in the error you're getting.
Possible solutions:
Use a before filter—Execution of the current action is halted if a before filter triggers a redirect. This is standard Rails practice.
before_filter :check_for_current_user, only: [:new]
def new
#user = User.new
respond_to do |format|
format.html # new.html.erb
format.json { render json: #user }
end
end
protected
def check_for_current_user
redirect_to(action: 'home') if #current_user
end
Just return early.
def new
if #current_user
redirect_to(action: 'home') and return
end
#user = User.new
respond_to do |format|
format.html # new.html.erb
format.json { render json: #user }
end
end
Cite: http://excid3.com/blog/execution-after-redirect-vulnerability