(PDOC-53) Handle directives with no types

Parameter directives with no types will have `tag.type` set to nil. We cannot
append nil to an array, so instead, place it in the array and flatten the
array. If the property is empty the second entry in the array will be nil, as
we expect. If the `tag.type` is an array of types we will have and array with
the form:
	[tag.text, type1, type2, type3, ...]

lib/puppet_x/puppetlabs/strings/yard/tags/directives.rb

@@ -3,7 +3,7 @@ require 'puppet_x/puppetlabs/strings/yard/core_ext/yard'
 class PuppetX::PuppetLabs::Strings::YARD::Tags::PuppetTypeParameterDirective < YARD::Tags::Directive
   def call
     return if object.nil?
-    object.parameters << ([tag.text] + tag.types)
+    object.parameters << ([tag.text, tag.types].flatten)
     object.parameter_details << {:name => tag.name, :desc => tag.text, :exists? => true, :puppet_type => true}
   end
 end