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

source.go

@@ -25,7 +25,7 @@ type Source struct {
 
 // NewSource creates a new Source. It returns a *Source.
 func NewSource() *Source {
-	return new(Source)
+	return &Source{CommonAttributes: newCommonAttributes()}
 }
 
 // Check checks the Source for incompatibilities with RFC4287. It returns an