code: public static AnnotationValue getAnnotationValue(
        AnnotationMirror annotationMirror, String elementName) {
      return getAnnotationElementAndValue(annotationMirror, elementName).getValue();
    }
docs: Returns an {@link AnnotationValue} for the named element if such an element was
  either declared in the usage represented by the provided {@link AnnotationMirror}, or if
  such an element was defined with a default.
  
  @throws IllegalArgumentException if no element is defined with the given elementName.