title: JPA - Extending java String,Date
body: <p>Is it possible to declare a type</p>
  
  <pre><code>@????? // Embeddable? 
  class MyDate extends java.util.Date implements Serializable{
  
      //.. lots of logic, but no new fields
  
  }
  </code></pre>
  
  <p>and include it in a mapping</p>
  
  <pre><code>class Person {
  
     @????
     MyDate birthdate;
  
  }
  </code></pre>
  
  <p>I have tried Embeddable/Embedded but I get this error message</p>
  
  <pre><code>[junit] 7109  venses  WARN   [main] openjpa.MetaData - "birhtdate" declares a null indicator column ""birthdate_null"" whose JDBC type is not compatible with the expected type "integer".
  </code></pre>