when sorting using <...tal:repeat subsection python:sequence.sort(subsections,(('title','nocase','asc'),))">

I get the following error:

Module DocumentTemplate.sequence.SortEx, line 134 in nocase

AttributeError: 'NoneType' object has no attribute 'lower'

When I switch the 'nocase' to 'cmp' the sort defaults to sorting by order
of entry or something.

Any help would be greatly appreciated.

Thanks.