Help needed with "Fields 'xxx' are not a default persistent type" warning

[Glen Mazza]

Hi, I'm new to OpenJPA (and JPA) and trying to create the entity-mapping 
XML files (classes are unannotated POJOs) for a simple parent-child 
database relationship[1] (parent is department, child is employees 
working at that department)  Right now, here's what I have for the 
mapping files:[2] (classes are here: [3]).

While my TestClass[4] (which accesses just the department table right 
now) runs fine I'm getting this warning message while running it:
"2213  CompanyPU  WARN   [main] openjpa.Runtime - Fields "employees" are 
not a default persistent type, and do not have any annotations 
indicating their persistence strategy. They will be treated as 
non-persistent. If you intended for these fields to be persistent, be 
sure to annotate them appropriately. Otherwise annotate them with 
@Transient."

Google is returning many examples of others with this error, but I'm 
still not sure what I'm doing wrong.  In the department.orm.xml, I can't 
map "employees" as Transient because it is already mapped as 
<one-to-many/>, which is AFAICT the right mapping to do. Basically, what 
do I have to fix my department.orm.xml[2] (or Department.java class[3]) 
in order to get rid of the above warning message?

Thanks,
Glen


[1] 
https://github.com/gmazza/blog-samples/blob/master/jpa_and_junit/src/main/config/create-database-derby.sql
[2] 
https://github.com/gmazza/blog-samples/tree/master/jpa_and_junit/src/main/resources/entities
[3] 
https://github.com/gmazza/blog-samples/tree/master/jpa_and_junit/src/main/java/entities
[4] 
https://github.com/gmazza/blog-samples/blob/master/jpa_and_junit/src/main/java/TestClass.java