It's fairly common to define a JPA data model in a completely separate project, and have your EJBs/application depend on that model project. That way, you can have multiple versions of the same model which map to different database schemata, and your EJBs can target a particular schema simply by depending on the appropriate model project.

In this case, the model project does not and should not contain a persistence unit, since it's defined in the EJB. Please lower the warning level of the "The project does not contain a persistence unit" hint to "warning on current line", or make this configurable.