has_one :scope
  accepts_nested_attributes_for :scope

belongs_to :project
has_one :participant
accepts_nested_attributes_for :participant,

belongs_to :scope
  has_one :address
  accepts_nested_attributes_for :address

belongs_to :participant

<%= f.simple_fields_for :participant do |partadd_p| %>
      <%= partadd_p.simple_fields_for :address do |partadd| %>



            <div class="row">
              <div class="col-md-3 col-md-offset-1">
                <%= partadd.label 'Select participation location', :class => 'question-project' %>
              </div>
              <div class="col-md-7">
                <div class="response-project">

                  <%= partadd.input :participant_country, priority: ["AU", "NZ", "GB", "US"], label: false %>

<%= render 'addresses/partform', f: f %>

<div id="participationrequest" style="display:none">
    <%= render 'participants/form', f: f %>
  </div>

<% if @project.scope.try(:if_participant) == true %>
        <%= render 'participants/particulars'%>
    <% end %>

<% if @project.scope.participant.location_specific == true %>
        <%= @project.scope.participant.address.participation_country %>
      <% else %>
        <%= render :text => "Remote participation" %>
      <% end %>

undefined method `participation_country' for nil:NilClass

<%= @project.scope.try(:participant).try(:address).try(:participation_country) %>

def new
    @participant = Participant.new
    @participant.address = Address.new

  end

@project.scope.participant = Participant.new