First argument cannot contain nil or be empty rails 4 - ruby-on-rails-4

Question

I'm making a single page application based on Futureme.org for practice. The user goes to the home page, sees a form to put their email address, subject, and the body of their message and sends it.
The problem I am having is I get an error "First argument in form cannot contain nil or be empty". Here is my code;
Model;
class Letter < ActiveRecord::Base
VALID_EMAIL_REGEX = /\A[\w+\-,]+#[a-z\d\-.]+\.[a-z]+\z/i
validates_presence_of :email, presence: true, format: { with: VALID_EMAIL_REGEX },
uniqueness: { case_sensitive: false }
validates_length_of :subject, presence: true, length: { maximum: 50 }
validates_presence_of :message
end
Controller;
class LettersController < ApplicationController
def new
#letter = Letter.new
end
def create
#letter = Letter.new(params[:letter])
if #letter.save
redirect_to letters_path, :notice => "Your letter was sent!"
else
render "new"
end
end
end
View form;
<%= form_for #letter, :html => {:class => 'form-horizontal'} do |f| %>
<% if #letter.errors.any? %>
<div class="error_messages">
<h2><%= pluralize(#letter.errors.count, "error")%>stopped this message from being saved</h2>
<ul>
<% #letter.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
<% end %>
<div class="field">
<%= f.label :email %><br />
<%= f.text_field :email %>
</div>
<div class="field">
<%= f.label :subject %><br />
<%= f.text_field :subject %><br />
</div>
<div class="field">
<%= f.label :message, "Message" %><br />
<%= f.text_area :message, size: "60x10" %>
</div>
<div class="actions"><%= f.submit "Submit", class: "btn btn-small btn-primary" %></div>
<% end %>
The form is on the home page which is in the "Welcome Controller".
Any help would be great.

Answer 1

It looks like you build letter in action new when form is drawn on other view :)
You should move #letter = Letter.new to appropriate action
One of the variant is:
#WelcomeController
def home
#letter = Letter.new
end
#LettersController
def create
#letter = Letter.new(params[:letter])
if #letter.save
redirect_to letters_path, :notice => "Your letter was sent!"
else
render "welcome/home"
end
end
be careful if you prepare some data in action home you should care about initializing them for action create when validation failed because you render "welcome/home" view