I'm surprised that the [`Puppet::Property::List`](https://github.com/puppetlabs/puppet/blob/master/lib/puppet/property/list.rb#L58) doesn't strip elements in the array. If we had this same issue previously, then I wouldn't worry about it now, perhaps file a bug for future consideration.

If it's a new issue, then we could handle this in the `munge` method for the property, e.g.

<pre>
newproperty(:members, ...) do
  munge do |values|
    values.map(&:strip)
  end
end
</pre>