Gae exception: Object Manager has been closed

Root cause:
Org. datanucleus. Exceptions. nucleus ususerexception: Object Manager has been closed

Are you using Google App Engine for Java and JDO?
If you ask for a list of something you might have to call the method size (). (studip I know)

Thecode below wocould throw org. datanucleus. Exceptions. nucleus ususerexception: "Object Manager has been closed" if we removed the call to size ()

public list getallcustomers ()
{< br> List customers = new arraylist () ;
persistencemanager PM = pmfinstance. getpersistencemanager ();
string query = "select from" + customer. class. getname ();
MERs = (list pm.newquery(query0000.exe cute ();
MERs. size ();
PM. close ();
return customers;
}