Filebeat ERB templates don't handle Undef / False properly

[vollmerk]

ERB templates don't behave as expected with Undef using Puppet Server/Agent 6.x

$logstash = Undef
$elasticsearch = false
class { 'filebeat':
 outputs => {
   'logstash' => $logstash,
   'elasticsearch' => $elasticsearch,
 },
}

Results in an outputted Yaml file containing

output:
 logstash: !ruby/object:puppet::Pops::Types::PUndefType {}
 elasticsearch: false

Expected behavior would be

 output:

Cleanest solution would likely be switching to EPP, so there aren't weird typing issues between Puppet & Ruby. I can submit a pull request, if this is aggreable (it's a bit of work)