error using association.build

gistfile1.rb

Models:

class VpnConfig < ActiveRecord::Base
...
  has_many :vpn_accessible_local_nets, :dependent => :destroy

class VpnAccessibleLocalNet < ActiveRecord::Base
...

  belongs_to :vpn_config

Controller:

class VpnConfigsController < ApplicationController
...
  def new
    @vpn_config = VpnConfig.new
...    
    1.times do
      phase1 = @vpn_config.build_vpn_phase1_config
      phase2 = @vpn_config.build_vpn_phase2_config
      anet = @vpn_config.vpn_accessible_local_nets.build       <--------------
    end

Error:

NoMethodError (undefined method `build' for []:Array):
  app/controllers/vpn_configs_controller.rb:32:in `new'
  app/controllers/vpn_configs_controller.rb:29:in `times'
  app/controllers/vpn_configs_controller.rb:29:in `new'