private static final String PERSISTENCE_UNIT_NAME = "JPAtest";
  private static EntityManagerFactory factory;

  public static void main(String[] args) {
    factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
    EntityManager em = factory.createEntityManager();

    // create new todo
    em.getTransaction().begin();
    ToDo todo = new ToDo();
    todo.setSummary("This is a test");
    todo.setDescription("This is a test");
    //Error is here at persist();
    em.persist(todo);
    em.getTransaction().commit();

    Query q = em.createQuery("select * from ToDo");
    List<ToDo> todoList = q.getResultList();
    System.out.println(todoList);
    for (ToDo to : todoList) {
      System.out.println(to);
    }
    System.out.println("Size: " + todoList.size());

    em.close();
  }

at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:331)
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:288)
at oracle.jdbc.driver.T4C8Oall.receive(T4C8Oall.java:743)
at oracle.jdbc.driver.T4CPreparedStatement.doOall8(T4CPreparedStatement.java:216)
at oracle.jdbc.driver.T4CPreparedStatement.executeForDescribe(T4CPreparedStatement.java:799)
at oracle.jdbc.driver.OracleStatement.executeMaybeDescribe(OracleStatement.java:1038)
at oracle.jdbc.driver.T4CPreparedStatement.executeMaybeDescribe(T4CPreparedStatement.java:839)
at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1133)
at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(OraclePreparedStatement.java:3285)
at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:3329)
at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeSelect(DatabaseAccessor.java:1009)
at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.basicExecuteCall(DatabaseAccessor.java:644)
... 30 more