[Mimedefang] greylist filter error

[Xiaoyan Ma]

I borrowed David and Lucas' greylist code and tested on one box first it 
didn't generate any error but when implemented the same filter to another 
box I got the following error message in the log:

mimedefang-multiplexor: [ID 980602 mail.info] Slave 4 stderr: Use of 
uninitialized value in numeric eq (==) at /etc/mail/mimedefang-filter line 
141, <STDIN> line 35.

Here is the related part of code:

    lock_db();
     tie %hash, 'DB_File', $DBFilename;
     my $ret = ++$hash{$key};
     untie %hash;
     unlock_db();
     return ($ret == 1); #line 141
....

Any suggestions ?

Thanks.
Xiaoyan