[Boston.pm] DBI problem with mod_perl application (more)

I am running a mod_perl application that makes calls to the Oracle XMl
dbi interface (XML::Generator::DBI) . The Apache log file shows the 
following error
Use of uninitialized value in string eq at 
/usr/lib/perl5/site_perl/5.8.5/XML/Generator/DBI.pm line 180
The same error is at line 187.

The code at this point in DBI.pm is :

        my $ind = 0;
        while ($el_stack[$ind] eq $stack[$ind] and
               $ind <= $stack_len and
               $ind <= $el_stack_len)
        {
            $ind ++;
        }

        if ($el_stack[$ind] eq $stack[$ind] and $el_stack_len == 
$stack_len) {
            # We're already at the end of the stack, so output the column
            $proxy->send_tag($names->[$i], $row->[$i],
                            $encoding->[$i] ?
                                ('dbi:encoding' => $encoding->[$i])
                                :
                                ()
            ) if defined($row->[$i]);
        }


Line 180 is the while statement

Any suggestions on how to debug this ?