RS in a table sort if the objects are of different types

2014-05-04 17:40:44,164 [ajp-bio-8021-exec-8137] ERROR OLATRuntimeException - OLAT::ERROR ^%^ N1-E1551 ^%^ org.olat.core.logging ^%^  
https://lms.uni-kiel.de/auth/1%3A1%3A0%3A0%3A0/
Mozilla/5.0 (Windows NT 6.2; WOW64; rv:28.0) Gecko/20100101 Firefox/28.0
**RedScreen** java.lang.String cannot be cast to java.lang.Integer
<dispatchinfo>
	<componentinfo>
		<compname>table</compname>
		<compclass>org.olat.core.gui.components.table.Table</compclass>
		<extendedinfo>n/a</extendedinfo>
		<event>	 </event>
	</componentinfo>
	<controllerinfo></controllerinfo>
</dispatchinfo>
>>> stack of 1.cause::org.olat.core.logging.OLATRuntimeException: java.lang.String cannot be cast to java.lang.Integer
-> at org.olat.core.gui.exception.ExceptionWindowController.<init>(ExceptionWindowController.java:115)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:57)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:46)
   at org.olat.core.gui.components.Window.dispatchRequest(Window.java:516)
   at org.olat.core.gui.components.Window.doDispatchRequest(Window.java:228)
   at org.olat.core.gui.components.Component.dispatchRequest(Component.java:192)
   at org.olat.dispatcher.AuthenticatedDispatcher.processValidDispatchURI(AuthenticatedDispatcher.java:241)
   at org.olat.dispatcher.AuthenticatedDispatcher.execute(AuthenticatedDispatcher.java:197)
   at org.olat.core.servlets.OpenOLATServlet.executeUserRequest(OpenOLATServlet.java:261)
   at org.olat.core.servlets.OpenOLATServlet.doPost(OpenOLATServlet.java:211)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
>>> stack of 2.cause::java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
-> at java.lang.Integer.compareTo(Unknown Source)
   at org.olat.core.gui.components.table.DefaultColumnDescriptor.compareTo(DefaultColumnDescriptor.java:183)
   at org.olat.core.gui.components.table.TableComparator.compare(TableComparator.java:43)
   at org.olat.core.gui.components.table.TableComparator.compare(TableComparator.java:29)
   at java.util.TimSort.binarySort(Unknown Source)
   at java.util.TimSort.sort(Unknown Source)
   at java.util.TimSort.sort(Unknown Source)
   at java.util.Arrays.sort(Unknown Source)
   at java.util.Collections.sort(Unknown Source)
   at org.olat.core.gui.components.table.Table.resort(Table.java:584)
   at org.olat.core.gui.components.table.Table.dispatchRequest(Table.java:391)