code: public static AnnotationNode addAnnotationOrGetExisting(ClassNode classNode, Class<? extends Annotation> annotationClass) {
          return addAnnotationOrGetExisting(classNode, annotationClass, Collections.<String, Object>emptyMap());
      }
docs: Adds an annotation to the given class node or returns the existing annotation
  
  @param classNode The class node
  @param annotationClass The annotation class