Mass subscription error: Trying to get property of non-object in simplenews_realname_subscription_list_add_submit

Whenever trying to use the mass subscription functionality I get the following errors (screenshot attached):

Notice: Trying to get property of non-object in simplenews_realname_subscription_list_add_submit() (line 281 of /mydomain/public_html/drupal/sites/all/modules/simplenews_realname/simplenews_realname.module).

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'tid' cannot be null: INSERT INTO {simplenews_subscription} (tid, snid, status, timestamp, source) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4); Array ( [:db_insert_placeholder_0] => [:db_insert_placeholder_1] => 19 [:db_insert_placeholder_2] => 1 [:db_insert_placeholder_3] => 1361536278 [:db_insert_placeholder_4] => ) in simplenews_subscription_save() (line 1501 of /mydomain/public_html/drupal/sites/all/modules/simplenews/simplenews.module).

Tried debugging those lines of code both in simplenews.module and simplenews_realname.module but no success.
Any help would be greatly appreciated!