Strange behavior in session context object

[kingdom119]

As my project has to switch between two database,so I extend EntityManagerFactory.But in my customized class, we faced a very strange behavior. First I'd like to show my code first.

@Scope(ScopeType.APPLICATION)
public class DdsEntityManagerFactory extends EntityManagerFactory {

     @In
     private CurrentUserInformation currentUserInformation;

     private static Map<String, javax.persistence.EntityManagerFactory> factorys;

     @Unwrap
     public javax.persistence.EntityManagerFactory getEntityManagerFactory() {
          if (!DdsUtil.isNotEmptyString(currentUserInformation
                    .getSelectedDataBase().getDatabaseUnitName())) {
               currentUserInformation.getSelectedDataBase().setDatabaseUnitName(
                         super.getPersistenceUnitName());
          }

          if (factorys.containsKey(currentUserInformation.getSelectedDataBase()
                    .getDatabaseUnitName())) {
               return factorys.get(currentUserInformation.getSelectedDataBase()
                         .getDatabaseUnitName());
          }
          return null;
     }

     @Create
     public void startup(Component component) throws Exception {
          Map<String, Database> dbs = DatabaseCfgBundleLoader
                    .getDatabasesFromProperties();
          factorys = new HashMap<String, javax.persistence.EntityManagerFactory>();
          for (Database db : dbs.values()) {
               if (!factorys.containsKey(db.getDatabaseUnitName())) {
                    super.setPersistenceUnitName(db.getDatabaseUnitName());
                    factorys.put(db.getDatabaseUnitName(), super
                              .createEntityManagerFactory());
               }
          }
     }...........................

here is the code of CurrentUserInformation class:

@Name("currentUserInformation")
@Scope(ScopeType.SESSION)
@AutoCreate
public class CurrentUserInformation extends Identity implements Serializable {
     private static final long serialVersionUID = 1L;

     @SuppressWarnings("unused")
     @Logger
     private Log log;

     private User currentUser;

     private Trial selectedTrial;

     private Database selectedDataBase;
...........................

OK, normally,my project will works well.But sometimes, it will throw nullpointer exception at
if (!DdsUtil.isNotEmptyString(currentUserInformation
                    .getSelectedDataBase().getDatabaseUnitName()))
or if (factorys.containsKey(currentUserInformation.getSelectedDataBase()
                    .getDatabaseUnitName()))

But, how will this happen? my currentUserInformation has session context. Why it lose value sometimes.Please help.thanks.