[flexcoders] Sorting problem on date and numbers with null values, I think

[aceoohay]

I running flexbuilder 2.0.1, AS 3.

I have a number of datagrids. In two of my grids I have date and 
number fields that sometimes have no values returned from the DB. 
When I click the heading on these columns to sort Ascending they work 
fine. When I click a second time (descending) I get the following 
error;

===============================================================
Error: Cannot determine comparator for SortField with 
name ''MyNumberDataField''.
        at mx.collections::SortField/::nullCompare()
        at 
mx.collections::SortField/http://www.adobe.com/2006/flex/mx/internal::
internalCompare()
        at mx.collections::Sort/::internalCompare()
        at mx.collections::Sort/findItem()
        at mx.collections::ListCollectionView/getItemIndex()
        at ::ListCollectionViewCursor/::collectionEventHandler()
        at 
flash.events::EventDispatcher/flash.events:EventDispatcher::dispatchEv
entFunction()
        at flash.events::EventDispatcher/dispatchEvent()
        at mx.collections::ListCollectionView/dispatchEvent()
        at mx.collections::ListCollectionView/::internalRefresh()
        at mx.collections::ListCollectionView/refresh()
        at mx.controls::DataGrid/::sortByColumn()
        at mx.controls::DataGrid/::headerReleaseHandler()
        at 
flash.events::EventDispatcher/flash.events:EventDispatcher::dispatchEv
entFunction()
        at flash.events::EventDispatcher/dispatchEvent()
        at mx.core::UIComponent/dispatchEvent()
        at mx.controls::DataGrid/mx.controls:DataGrid::mouseUpHandler
()
===============================================================

I am not using a sort compare function anywhere. I have other text 
type fields with nulls that seem to sort correctly.

This seems like a bug. 

Any ideas?

Paul