[Zope] len() of unsized object

I have the following DTML code: <dtml-in ZSQL_method> <dtml-if email2><dtml-var email2></dtml-if> </dtml-in> ZSQL_method is a select * where key=xxx and gives exactly one row. Zope gives the following error: Error Type: TypeError Error Value: len() of unsized object It is only produced if email2 is not NULL. If I include email2 without the test it works - but then I include also NULL values. The error is also generated if I use <dtml-if "_['sequence-item'].email2"> I looked at this error type and found only references to some odd sendmail tag behaviour. Can anybody give me a hint, where to look and what to look for? Software: MySQL 3.22.32 Zope 2.3.0 MySQLDA 2.0.4 Python 1.52 Regards, Frank