diff --git a/manifests/node.pp b/manifests/node.pp
index 99c952f..f7fd638 100644
--- a/manifests/node.pp
+++ b/manifests/node.pp
@@ -1,127 +1,127 @@
 # munin::node - Configure a munin node, and export configuration a
 # munin master can collect.
 #
 # Parameters:
 #
 # allow: List of IPv4 and IPv6 addresses and networks to allow to connect.
 #
 # config_root: Root directory for munin configuration.
 #
 # nodeconfig: List of lines to append to the munin node configuration.
 #
 # host_name: The host name munin node identifies as. Defaults to
 # the $::fqdn fact.
 #
 # log_dir: The log directory for the munin node process. Defaults
 # change according to osfamily, see munin::params::node for details.
 #
 # masterconfig: List of configuration lines to append to the munin
 # master node definitinon
 #
 # mastername: The name of the munin master server which will collect
 # the node definition.
 #
 # mastergroup: The group used on the master to construct a FQN for
 # this node. Defaults to "", which in turn makes munin master use the
 # domain. Note: changing this for a node also means you need to move
 # rrd files on the master, or graph history will be lost.
 #
 # plugins: A hash used by create_resources to create munin::plugin
 # instances.
 #
 # address: The address used in the munin master node definition.
 #
 # package_name: The name of the munin node package to install.
 #
 # service_name: The name of the munin node service.
 #
 # service_ensure: Defaults to "". If set to "running" or "stopped", it
 # is used as parameter "ensure" for the munin node service.
 #
 # export_node: "enabled" or "disabled". Defaults to "enabled".
 # Causes the node config to be exported to puppetmaster.
 #
 # file_group: The UNIX group name owning the configuration files,
 # log files, etc.
 
 class munin::node (
   $address        = $munin::params::node::address,
   $allow          = $munin::params::node::allow,
   $config_root    = $munin::params::node::config_root,
   $host_name      = $munin::params::node::host_name,
   $log_dir        = $munin::params::node::log_dir,
   $masterconfig   = $munin::params::node::masterconfig,
   $mastergroup    = $munin::params::node::mastergroup,
   $mastername     = $munin::params::node::mastername,
   $nodeconfig     = $munin::params::node::nodeconfig,
   $package_name   = $munin::params::node::package_name,
   $plugins        = $munin::params::node::plugins,
   $service_ensure = $munin::params::node::service_ensure,
   $service_name   = $munin::params::node::service_name,
   $export_node    = $munin::params::node::export_node,
   $file_group     = $munin::params::node::file_group,
 ) inherits munin::params::node {
 
   validate_array($allow)
   validate_array($nodeconfig)
   validate_array($masterconfig)
-  validate_string($mastergroup)
-  validate_string($mastername)
+  if $mastergroup { validate_string($mastergroup) }
+  if $mastername { validate_string($mastername) }
   validate_hash($plugins)
   validate_string($address)
   validate_absolute_path($config_root)
   validate_string($package_name)
   validate_string($service_name)
-  validate_re($service_ensure, '^(|running|stopped)$')
+  if $service_ensure { validate_re($service_ensure, '^(running|stopped)$') }
   validate_re($export_node, '^(enabled|disabled)$')
   validate_absolute_path($log_dir)
   validate_string($file_group)
 
   if $mastergroup {
     $fqn = "${mastergroup};${host_name}"
   }
   else {
     $fqn = $host_name
   }
 
-  if $service_ensure != '' { $_service_ensure = $service_ensure }
+  if $service_ensure { $_service_ensure = $service_ensure }
   else { $_service_ensure = undef }
 
   # Defaults
   File {
     ensure => present,
     owner  => 'root',
     group  => $file_group,
     mode   => '0444',
   }
 
   package { $package_name:
     ensure => installed,
   }
 
   service { $service_name:
     ensure  => $_service_ensure,
     enable  => true,
     require => Package[$package_name],
   }
 
   file { "${config_root}/munin-node.conf":
     content => template('munin/munin-node.conf.erb'),
     require => Package[$package_name],
     notify  => Service[$service_name],
   }
 
   # Export a node definition to be collected by the munin master
   if $export_node == 'enabled' {
     @@munin::master::node_definition{ $fqn:
       address    => $address,
       mastername => $mastername,
       config     => $masterconfig,
       tag        => [ "munin::master::${mastername}" ]
     }
   }
 
   # Generate plugin resources from hiera or class parameter.
   create_resources(munin::plugin, $plugins, {})
 
 }
diff --git a/manifests/params/node.pp b/manifests/params/node.pp
index 587733a..c319b04 100644
--- a/manifests/params/node.pp
+++ b/manifests/params/node.pp
@@ -1,70 +1,70 @@
 class munin::params::node {
 
   $message = "Unsupported osfamily: ${::osfamily}"
 
   $address        = $::fqdn
   $host_name      = $::fqdn
   $allow          = []
   $masterconfig   = []
-  $mastergroup    = ''
-  $mastername     = ''
+  $mastergroup    = undef
+  $mastername     = undef
   $nodeconfig     = []
   $plugins        = {}
-  $service_ensure = ''
+  $service_ensure = undef
   $export_node    = 'enabled'
 
   case $::osfamily {
     'RedHat': {
       $config_root  = '/etc/munin'
       $log_dir      = '/var/log/munin-node'
       $service_name = 'munin-node'
       $package_name = 'munin-node'
       $plugin_share_dir = '/usr/share/munin/plugins'
       $file_group   = 'root'
     }
     'Debian': {
       $config_root  = '/etc/munin'
       $log_dir      = '/var/log/munin'
       $service_name = 'munin-node'
       $package_name = 'munin-node'
       $plugin_share_dir = '/usr/share/munin/plugins'
       $file_group   = 'root'
     }
     'Solaris': {
       case $::operatingsystem {
         'SmartOS': {
           $config_root  = '/opt/local/etc/munin'
           $log_dir      = '/var/opt/log/munin'
           $service_name = 'smf:/munin-node'
           $package_name = 'munin-node'
           $plugin_share_dir = '/opt/local/share/munin/plugins'
           $file_group   = 'root'
         }
         default: {
           fail("Unsupported operatingsystem ${::operatingsystem} for osfamily ${::osfamily}")
         }
       }
     }
     'FreeBSD', 'DragonFly': {
       $config_root  = '/usr/local/etc/munin'
       $log_dir      = '/var/log/munin'
       $service_name = 'munin-node'
       $package_name = 'munin-node'
       $plugin_share_dir = '/usr/local/share/munin/plugins'
       $file_group   = 'wheel'
     }
     'OpenBSD': {
       $config_root  = '/etc/munin'
       $log_dir      = '/var/log/munin'
       $service_name = 'munin_node'
       $package_name = 'munin-node'
       $plugin_share_dir = '/usr/local/libexec/munin/plugins'
       $file_group   = 'wheel'
     }
     default: {
       fail($message)
     }
   }
 }