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

[Lunixer]

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

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