private ImmutableMap<String, AnnotationValue> getDefaultValues(TypeElement annotationElement) {
    ImmutableMap.Builder<String, AnnotationValue> defaultValues = ImmutableMap.builder();
    for (ExecutableElement member :
        ElementFilter.methodsIn(annotationElement.getEnclosedElements())) {
      String name = member.getSimpleName().toString();
      AnnotationValue defaultValue = member.getDefaultValue();
      if (defaultValue != null) {
        defaultValues.put(name, defaultValue);
      }
    }
    return defaultValues.build();
  }
Returns a map from the names of members with invariable hashCodes to the values of those
hashCodes.
value/src/main/java/com/google/auto/value/processor/AutoAnnotationProcessor.java