[Puppet Users] puppet template syntax problem: undefined method `each' for nil:NilClass

I was going through the Puppet Learning doc.
Got to the template section and the ERB file, which is using the 'each'
method to print the $real_servers.
The puppet run fails with pointing to the 'each' method.
Is this a bug? does anyone have any pointers?

Using:
centos 6.6
puppet 3.8.1
ruby 1.8.7

Thanks.

# cat /etc/puppet/modules/ntp/manifests/init.p
class ntp {

     # Choose platform, package name, and config file name
     case $operatingsystem {
         centos, redhat: {
             $service_name = 'ntpd'
             $conf_file = 'ntp.conf'
             $default_servers = [ "0.centos.pool.ntp.org",
                                  "1.centos.pool.ntp.org",
                                  "2.centos.pool.ntp.org", ]
         }
         debian, ubuntu: {
             $service_name = 'ntp'
             $conf_file = 'ntp.conf.debian'
             $default_servers = [ "0.debian.pool.ntp.org iburst",
                                  "1.debian.pool.ntp.org iburst",
                                  "2.debian.pool.ntp.org iburst",
                                 "3.debian.pool.ntp.org iburst", ]
         }
         default: { fail("Unrecognized operating system for webserver") }
     }

     $servers_real = $default_servers

     # Install the package
     package { 'ntp':
         ensure => installed,
     }

     # Get the config file
     file { 'ntp.conf':
         path => '/etc/ntp.conf',
         ensure => file,
         require => Package['ntp'],
         content => template("ntp/${conf_file}.erb"),
     }

     # Manage the service
     service { 'ntp':
         name => $service_name,
         ensure => running,
         enable => true,
         subscribe => File['ntp.conf'],
     }

} #class



# cat /etc/puppet/modules/ntp/templates/ntp.conf.erb
<% @servers_real.each do |this_server| -%>
server <%= this_server %>
<% end -%>


# puppet agent --test
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Loading facts
Error: Could not retrieve catalog from remote server: Error 400 on SERVER:
Failed to parse template ntp/ntp.conf.erb:
   Filepath: /etc/puppet/modules/ntp/templates/ntp.conf.erb
   Line: 2
   Detail: undefined method `each' for nil:NilClass
  at /etc/puppet/modules/ntp/manifests/init.pp:26 on node
puppetmaster.example.com
Warning: Not using cache on failed catalog
Error: Could not retrieve catalog; skipping run