My app is throwing a random undefined method `map' for nil:NilClass error

Question

I'm currently creating a job board and in my listings/new.html.erb file and I have a section within the form for people to choose a category. The category is its own separate model.

But when I submit the form I get a 'undefined method `map' for nil:NilClass' error.

Below are my models, controllers, and the part of the view which is appropriate. Thank you ahead of time.

_form.html.erb

<div class="form-group">
<h4>Job Category:</h4>
  <%= form.select(:category_id, options_for_select(@categories)) %>
</div>

listings_controller.rb

def new
  @listing = Listing.new
  @categories = Category.all.map{|c| [ c.title, c.id ] }
end

def create
@categories = Category.all.map{|c| [ c.title, c.id ] }
@listing = Listing.new(listing_params)
@listing.category_id = params[:category_id]
charge_error = nil

if @listing.valid?
  begin
    customer = Stripe::Customer.create(
      :email => 'example@stripe.com',
      :card => params[:stripeToken])

      charge = Stripe::Charge.create(
        :customer => customer.id,
        :amount => 150,
        :description => 'Job Posting via Remote Business Jobs',
        :currency => 'usd')

  rescue Stripe::CardError => e
    charge_error = e.message
  end
  if charge_error
    flash[:error] = charge_error
    render :new
  else
    @listing.save
    redirect_to @listing
  end
else
  flash[:error] = 'one or more errors in your orders'
  render :new
end
end
def listing_params
  params.require(:listing).permit(:title, :body, :apply_link, 
  :company_link, :employment_type, :company, :salary_range, 
  :category_id, 
 :slug, :hq)
end

listing.rb

class Listing < ApplicationRecord
 extend FriendlyId
 friendly_id :title, use: :slugged

 belongs_to :category

end

category.rb

class Category < ApplicationRecord
 extend FriendlyId
 friendly_id :title, use: :slugged

 has_many :listings
end

Edit Log: I updated the listings_controller.rb to include

@categories = Category.all.map{|c| [ c.title, c.id ] }

Answer 1

You're missing this line from your create action, just make sure it's before any render :new. This is needed because you're using this in the form in case something fails.

@categories = Category.all.map{|c| [ c.title, c.id ] }