JPA: Error loading the persistence descriptor WEB-INF/lib/_wl_cls_gen.jar!/META-INF/persistence.xml from the module

Root cause:
persistence.xml is located in src/main/resources/META-INF
Solution: 
move persistence.xml to src/main/java
That's it. Is that simple!?

Note: if you encounter an error, when trying to run a main (as Java application in Eclipse), then you need to move it back to src/main/resources/META-INF