Unclear message when removing user expiry

Example resource:

user { 'dragos':
ensure => 'present',
comment => 'dragos',
expiry => '1970-01-01',
gid => '120',
home => '/home/dragos',
password => 'here-goes-a-hash',
password_max_age => '99999',
password_min_age => '0',
shell => '/bin/bash',
uid => '1003',

If I'm setting the expiry via the manifests file as absent:

expiry => 'absent',

, will cause a --noop run to report that the current expiry value should be absent:

Notice: /Stage[main]/XXX::dragos/User[dragos]/expiry: current_value 1970-01-01, should be absent (noop)

, while an actual run will report an invalid expiry value:

Notice: /Stage[main]/XXX::dragos/User[dragos]/expiry: undefined 'expiry' from '1970-01-01'

The goal is to be able to remove the account expire date, for an account that already has a value set.