public static AnnotationValue getAnnotationValue(
      AnnotationMirror annotationMirror, String elementName) {
    return getAnnotationElementAndValue(annotationMirror, elementName).getValue();
  }
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.
common/src/main/java/com/google/auto/common/AnnotationMirrors.java