Apologies, this was due to not having strict mode on, the warning does appear as expected.
SHOW WARNINGS;
|
+---------+------+-------------------------------------------------------------------------------+
|
| Level | Code | Message |
|
+---------+------+-------------------------------------------------------------------------------+
|
| Warning | 4038 | Syntax error in JSON text in argument 1 to function 'json_keys' at position 1 |
|
+---------+------+-------------------------------------------------------------------------------+
|
Safe to re-close, unfortunately I can't do so.
http://lists.askmonty.org/pipermail/commits/2016-December/010270.html