La ligne suivante est manquante dans votre persistence.xml :
<exclude-unlisted-classes>false</exclude-unlisted-classes>
Cette ligne est placée comme dans l'exemple suivant :
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="SamplePU" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<exclude-unlisted-classes>false</exclude-unlisted-classes>
<properties>
<property name="javax.persistence.jdbc.url" value="jdbc:derby://localhost:1527/sample"/>
<property name="javax.persistence.jdbc.password" value="123"/>
<property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.ClientDriver"/>
<property name="javax.persistence.jdbc.user" value="root"/>
<property name="eclipselink.logging.level" value="ALL"/>
<property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
</properties>
</persistence-unit>
</persistence>
