Well, strictly speaking the spec only states BeanAttributes#getStereotypes() must return the bean stereotypes but the javadoc states:

@return the set of stereotypes

So in my opinion this method should never return null. Also I believe it's better to avoid using null if possible, esp. if the code/javadoc does not explicitly state it supports null.

Nevertheless, it seems the intention really was to return a set with PlainOldAnnotation literal.