which is consistent with other restrictions about using a class loader in your EJBs. The EJB Container is responsible for maintaining runtime environment, and it loads classes itself, applying security restrictions. If you violate these rules, the runtime environment will not be compliant.
This restriction is not about prohibiting to use packages for your EJB classes.
Exam 1Z0-817: Upgrade OCP Java 6, 7 and 8 to Java SE 11 Developer Study Guide and Quiz