Fix apt pin for new version of apt module

* Require package_apt_pin to be a non-empty string or number
* Use `nil` instead of empty string in test for empty pin

Author: wyardley

REFERENCE.md

@@ -725,7 +725,7 @@ Default value: `undef`
 
 ##### <a name="-rabbitmq--package_apt_pin"></a>`package_apt_pin`
 
-Data type: `Optional[Variant[Numeric, String]]`
+Data type: `Optional[Variant[Numeric, String[1]]]`
 
 Whether to pin the package to a particular source
 

manifests/init.pp

@@ -378,7 +378,7 @@
   Boolean $management_ssl                                                                          = true,
   Optional[String] $management_hostname                                                            = undef,
   Optional[String] $node_ip_address                                                                = undef,
-  Optional[Variant[Numeric, String]] $package_apt_pin                                              = undef,
+  Optional[Variant[Numeric, String[1]]] $package_apt_pin                                           = undef,
   String $package_ensure                                                                           = 'installed',
   Optional[String] $package_gpg_key                                                                = undef,
   Optional[String] $repo_gpg_key                                                                   = undef,

spec/classes/rabbitmq_spec.rb

@@ -83,7 +83,7 @@
       end
 
       context 'with no pin', if: os_facts['os']['family'] == 'Debian' do
-        let(:params) { { repos_ensure: true, package_apt_pin: '' } }
+        let(:params) { { repos_ensure: true, package_apt_pin: nil } }
 
         describe 'it sets up an apt::source' do
           it {