Unquoted boolean true statement in nagios_service type event_handler_enabled => true, causes error.

Unquoted boolean true statement in nagios_service type event_handler_enabled => true, causes error. 'true' in quotes evaluates properly.

"Could not evaluate: private method `sub' called for true:TrueClass"

i.e.
@@nagios_service {"${::hostname}_puppet":
host_name => $::hostname,
service_description => "${::hostname}_puppet",
check_command => "check_nrpe_1arg!check_puppet",
servicegroups => "puppet",
max_check_attempts => 5,
check_interval => 30,
retry_interval => 30,
check_period => '24x7',
notification_interval => 30,
notification_period => "24x7",
notification_options => 'n',
contact_groups => 'admins',
event_handler_enabled => true,
event_handler => 'puppet_handler',
target => "/etc/icinga/objects/puppet/service_${::hostname}_puppet.cfg",
}