Puppet Template Patterns to remember.

puppet-template-patterns.erb

## Check if variable is defined
# Replaces has_variable?(var) and if @var variations.
# include?() pattern from @Jan_vStone.
#
# scope.lookupvar return values for undefined variables:
# Puppet 3.x: nil
# Puppet 2.6.x: :undefined
# Puppet 2.7.x: :undefined
<% if ! [:undefined, nil, ''].include?(masquerade_address = scope.lookupvar('ftp::masquerade_address')) -%>
  MasqueradeAddress <%= masquerade_address %>
<% end -%>