( sent_email is NULL OR
  sent_email='0000-00-00');

##</code><code>##

  sent_email => {'!=', undef },
  sent_email => {'!=', '0000-00-00

##</code><code>##

my @proc_requests = $schema->resultset( 'TblRequests' )->search({
  -or =>[ status => 'Review' ,  
    -and => [ 
       -or => [
         status => 'Offered',
         status => 'Denied',
         status => 'Cancelled',
         status => 'Conditional Offer',
       ],
       -or => [
         sent_email => {'=', undef },
         sent_email => {'=', '0000-00-00'},
       ]
     ],
   ],  
  },
  { join => 'p' }
);