testing if a variable is EMPTY

I'd like to test if a variable has been set but has nothing as its  
contents.

I haven't been able to find any examples of this, but I'm sure it's  
a rather simple matter

All I want to do is:

if [ "$MyVar" = "" ]
then
        do this
else
        do that
fi

I don't know how to do that in procmailese.

TIA

TjL

--
        Tj Luoma (luomat(_at_)peak(_dot_)org)
                http://www.next.peak.org/~luomat
                        Awaiting Apple's NeXTStep