title: GenericGenerator not generating a value
body: <p>I've got an entity with a <code>@GenericGenerator</code>:</p>
  
  <pre><code>@Entity
  public class Report {
      @Id
      @GenericGenerator(name = "generator", strategy = "foreign",
              parameters = @Parameter(name = "property", value = "examrequisitions"))
      // @GeneratedValue(strategy = GenerationType.IDENTITY)
      @Basic(optional = false)
      @Column(nullable = false, unique = true)
      private Long id;
  
      ... // outcome, status
  }
  </code></pre>
  
  <p>When I save that entity it shows the following exception:</p>
  
  <pre><code>Caused by: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.DatabaseException
  Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'id' cannot be null
  Error Code: 1048
  Call: INSERT INTO SystemCardiologyReports.REPORTS (ID, OUTCOME, STATUS) VALUES (?, ?, ?)
      bind =&gt; [3 parameters bound]
  Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'id' cannot be null
  </code></pre>
  
  <p>Why is the ID <code>null</code> - despite the <code>@GenericGenerator</code>?</p>