title: "invalid stream header" exception - Lob with JPA and MySQL
body: <p>I have a field defined like this </p>
  
  <pre><code>@MappedSupperclass
  public abstract class BaseItem {
  
      ...
      @Lob @Basic(fetch=FetchType.EAGER)
      private String description;
      ...
  }
  
  @Entity
  public class Item extends BaseItem {
  }
  </code></pre>
  
  <p>I'm using MySQL 5  and the <code>desccription</code> field type is <code>TEXT</code>.</p>
  
  <p>While trying to read an object of type Item I get the following error:</p>
  
  <pre><code>java.io.StreamCorruptedException: invalid stream header: 6576656E
      at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:782)
      at java.io.ObjectInputStream.&lt;init&gt;(ObjectInputStream.java:279)
      at org.datanucleus.store.rdbms.datatype.BlobImpl.getObject(BlobImpl.java:121)
      at org.datanucleus.store.rdbms.mapping.AbstractLargeBinaryRDBMSMapping.getObjectForBytes(AbstractLargeBinaryRDBMSMapping.java:362)
      at org.datanucleus.store.rdbms.mapping.AbstractLargeBinaryRDBMSMapping.getObject(AbstractLargeBinaryRDBMSMapping.java:395)
      at org.datanucleus.store.mapped.mapping.AbstractContainerMapping.getObject(AbstractContainerMapping.java:228)
      at org.datanucleus.store.rdbms.fieldmanager.ResultSetGetter.fetchObjectField(ResultSetGetter.java:176)
      at org.datanucleus.state.AbstractStateManager.replacingObjectField(AbstractStateManager.java:2353)
      ...
  </code></pre>
  
  <p>Do you have any idea of what are the possible causes for this?</p>
  
  <p>I'm using JDK6 and DataNucleus 3.1.1.</p>