code: private static <T extends Annotation> Class<? extends Annotation>
        getRepeatableAnnotationContainerClassFor(Class<T> annotationClass) {
  
      Repeatable repeatableAnnotation = annotationClass.getDeclaredAnnotation(Repeatable.class);
      return (repeatableAnnotation == null) ? null : repeatableAnnotation.value();
    }
docs: Find the {@code \@Repeatable} container annotation class for an annotation class, or
  {@code null}.
  
  <p>
  Given:
  
  <code>
  @Repeatable(X.class)
  @interface SomeName {     <--- = annotationClass
  }...
  </code>
  
  <p>
  Returns {@code X.class}
  
  Otherwise if there was no {@code \@Repeatable} annotation, return {@code null}.
  </p>