This will prevent an email from sending if the content of the email is 'No Entries Found'.

add_filter('frm_send_email', 'frm_stop_email_with_no_entries', 10, 2);
function frm_stop_email_with_no_entries( $send, $email){
  if ($email['message'] == 'No Entries Found') {
    $send = false;
  }
  return $send;
}