ClassCastException with jetty and jpa

When I try to execute my application based on jersey, guice, and jpa on jetty (7.2.0 or 8.0.0.M1) I get the following error, even if I don't use JNDI.

    java.lang.ClassCastException: org.eclipse.jetty.jndi.NamingContext cannot be cast to javax.sql.DataSource

Caused by:

javax.persistence.PersistenceException: java.lang.ClassCastException: org.eclipse.j开发者_高级运维etty.jndi.NamingContext cannot be cast to javax.sql.DataSource
    at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:397)
    at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.getServerSession(EntityManagerFactoryImpl.java:151)
    at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:207)
    at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:195)
...

Here is the corresponding persistence.xml

<?xml version="1.0" encoding="UTF-8"?>

<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence  http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  <persistence-unit name="myproject" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:derby:memory:mydb;create=true"/>
      <property name="javax.persistence.jdbc.password" value=""/>
      <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.EmbeddedDriver"/>
      <property name="javax.persistence.jdbc.user" value=""/>
      <property name="eclipselink.ddl-generation" value="create-tables"/>
    </properties>
    <non-jta-data-source/>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
  </persistence-unit>
</persistence>

Any ideas?

You don't need <non-jta-data-source/> since you don't use JNDI.