Fix rare undefined method `any?' for nil:NilClass error. Fixes #287

In some rare cases where no parameter is (yet) defined in the type, an error is thrown

```
Error: undefined method `any?' for nil:NilClass
```

Author: hajee

lib/puppet-strings/yard/code_objects/type.rb

@@ -148,6 +148,7 @@ def add_check(check)
   end
 
   def parameters
+    @parameters ||= []  # guard against not filled parameters
     # just return params if there are no providers
     return @parameters if providers.empty?