[Zope] How to cat strings together that may be NULL?

[Greg]

    I am trying to cat several fields together into one string from a 
mysql table.  I keep getting an error about "Cannot add type "None" to 
string".  I am guessing that some of my feilds are NULL.  My goal is to 
copy the columns from one table and dump them into one column of another.

I have this:

<dtml-in sqlGetTableColumns>
    <dtml-call "REQEST.set('tbldata', Field1, Field2, Field3, Field4)">
    <dtml-call "sqlInsertDump(DumpCol=tbldata,User=AUTHENTICATED_USER)">
</dtml-in>

Field3 and Field4 are usually NULL, but not always, so I want to capture 
them as well.

Any suggestions?

Thanks!

Greg