Getting undefined method 'map' for Nil Class (coming from Kind.all on the select_options method)

_form.html.erb

<%= form_for(@contact, html: { class: "basic-grey" }) do |f| %>
  <% if @contact.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@contact.errors.count, "error") %> prohibited this contact from being saved:</h2>

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

  <h1>Contacts</h1>

  <div class="field">
    <%= f.label :name %><br>
    <%= f.text_field :name %>
  </div>
  <div class="field">
    <%= f.label :email %><br>
    <%= f.text_field :email %>
  </div>
  <div class="field">
    <%= f.label :kind_id %><br>
    <%= collection_select(:contact, :kind_id, @kind_options_for_select, :id, :description) %>
  </div>


  <%= f.fields_for :address do |address_fields| %>
    <div class="field">
      <%= f.label :street %><br>
      <%= address_fields.text_field :street %>
    </div>
    <div class="field">
      <%= f.label :city %><br>
      <%= address_fields.text_field :city %>
    </div>
    <div class="field">
      <%= f.label :state %><br>
      <%= address_fields.text_field :state %>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :rmk %><br>
    <%= f.text_area :rmk %>
  </div>
  <div class="field">
    <%= f.submit "Enviar", class: "button" %>
    <%= link_to 'Back', contacts_path, class: "button"%>
  </div>
<% end %>

contact.rb

class Contact < ApplicationRecord
  belongs_to :kind
  has_one :address

  accepts_nested_attributes_for :address
end

contacts_controller.rb

class ContactsController < ApplicationController
  before_action :set_contact, only: [:show, :edit, :update, :destroy]

  # GET /contacts
  # GET /contacts.json
  def index
    @contacts = Contact.all
    @meu_nome = "Crova"
  end

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

  # GET /contacts/new
  def new
    @contact = Contact.new
    @contact.build_address

    options_for_select
  end

  # GET /contacts/1/edit
  def edit
    options_for_select
  end

  # POST /contacts
  # POST /contacts.json
  def create
    @contact = Contact.new(contact_params)
    @contact.build_address

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

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

  # DELETE /contacts/1
  # DELETE /contacts/1.json
  def destroy
    @contact.destroy
    respond_to do |format|
      format.html { redirect_to contacts_url, notice: 'Contact was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private

    def options_for_select
      @kind_options_for_select = Kind.all
    end


    # Use callbacks to share common setup or constraints between actions.
    def set_contact
      @contact = Contact.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def contact_params
      params.require(:contact).permit(:name, :email, :kind_id, :rmk, address_attributes: [:street, :city, :state])
    end
end
 

you're calling @kind_options_for_select directly from the form, but not the method that initializes it, as far as i can tell

I thought I was doing that on lines 21 and 26 of on the controller

you're doing it for new and edit actions which render the form initially, but you aren't doing it on create and update actions which both re-render the form in case of any input error

Ohh, I see, rookie mistake

Cheers mate