It looks like this was fixed along the way. Here is the current code and I am not seeing this error in trunk anymore.

package org.sakaiproject.tool.gradebook.facades.sakai2impl;
...
public class BaseEntityProducer implements EntityProducer {
//private static final Log log = LogFactory.getLog(BaseEntityProducer.class);

protected String label; // This should always be set.
protected String referenceRoot = "/gradebook"; // stupid default but OK since it is not used
protected String serviceName = null;
protected EntityManager entityManager;

public void setEntityManager(EntityManager entityManager) {
this.entityManager = entityManager;
}

/**

• Register this class as an EntityProducer.
  */
  public void init() {
  entityManager.registerEntityProducer(this, referenceRoot);
  }
  ...