Make python::dotfile::group optional

If the python class was not included in the catalog first,
python::params has not been loaded.  But this is not really critical,
just do as python::pip and allow undef values.

Author: smortex

REFERENCE.md

@@ -416,7 +416,7 @@ Default value: `'root'`
 
 ##### <a name="-python--dotfile--group"></a>`group`
 
-Data type: `String[1]`
+Data type: `Optional[String[1]]`
 
 group owner of dotfile
 

manifests/dotfile.pp

@@ -26,7 +26,7 @@
   Enum['absent', 'present'] $ensure   = 'present',
   Stdlib::Absolutepath      $filename = $title,
   String[1]                 $owner    = 'root',
-  String[1]                 $group    = getvar('python::params::group'),
+  Optional[String[1]]       $group    = getvar('python::params::group'),
   Stdlib::Filemode          $mode     = '0644',
   Hash                      $config   = {},
 ) {