@Override
    public void assign(Object o) {
        if (o != null && (!(o instanceof Annotation))) {
            throw new IllegalArgumentException("Cannot assign object of type " + o.getClass().getName() + " to an AnnotationReference, must be of type " + Annotation.class.getName());
        }
        setReference((Annotation) o);
    }
Returns the Annotation that this AnnotationReference refers to.

@return the Annotation that this AnnotationReference refers to.
document/src/main/java/com/yahoo/document/annotation/AnnotationReference.java