Instanciate common attributes everywhere so one can simply use the extend method

category.go

@@ -15,7 +15,10 @@ type Category struct {
 
 // NewCategory creates a new Category. It returns a *Category.
 func NewCategory(term string) *Category {
-	return &Category{Term: term}
+	return &Category{
+		CommonAttributes: newCommonAttributes(),
+		Term:             term,
+	}
 }
 
 // SetLabel sets the Label attribute of the Category.