ERROR - java.lang.IllegalArgumentException: Illegal attempt to dereference path source [null]

Using: JPA 2 with hibernate

Stacktrace:
java.lang.IllegalArgumentException: Illegal attempt to dereference path source [null]
at org.hibernate.ejb.criteria.path.AbstractPathImpl.illegalDereference(AbstractPathImpl.java:104)
at org.hibernate.ejb.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:186)

Cause:
I was doing a get on a PluralAttributePath

initial code:
Root root = criteriaQuery.from(Order.class);
Path path = root.get(key); //path to OrderLines
path = path.get("description"); //throws exception since Ordelines was a many to many join

new code:
Root root = criteriaQuery.from(Order.class);
Join join = criteriaQuery.join("orderLines");
Path path = root.get(key); //path to OrderLines
path = join.get("description");