Symbol into Hash error with Puppet 5.5.1

[GeoffWilliams]

Overview

When supplying a hash of rules to audit using a non-empty rules parameter, I always get a compile error.

Expected result

Expected no error

Actual result

There is something screwy going on with create_resources() that I don't understand. It's fallen out of favour to iteration these days since its harder to debug.

Error: Could not retrieve catalog from remote server: Error 500 on SERVER: Server Error: Evaluation Error: Error while evaluating a Resource Statement, Evaluation Error: Error while evaluating a Function Call, no implicit conversion of Symbol into Hash (file: /etc/puppetlabs/code/environments/production/modules/auditd/manifests/init.pp, line: 509, column: 5) on node XXX

Testcase

class { '::auditd':
  #  rules => { '-a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rules' => undef},
  rules => { 'foo' => undef }
}

Uncommenting either of the rules parameters results in above error.