gh-ost: getting Column 'message_id' cannot be null - while we have no null values in table.

Gettign the following error:

2018-02-12 15:35:05 ERROR Error 1048: Column 'message_id' cannot be null; query=
                        replace /* gh-ost `shoutout`.`_messages_gho` */ into
                                `shoutout`.`_messages_gho`
                                        (`message_id`, `instance_id`, `data`, `date_created`, `date_updated`, `short_code`, `status`, `tags`, `date_sent`, `distribution_status`)
                                values
                                        (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)

while: select count(1) from messages where message_id is null

    -> ;
+----------+
| count(1) |
+----------+
|        0 |
+----------+
1 row in set (0.00 sec)