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