Defaulted to a do-nothing 'parse error' gate. Failed to understand the json defining a gate.

URL
https://algassert.com/quirk#circuit=%7B%22cols%22:%5B%5B%22InputQubit%22,%22%22,%22%22,%22%7C0%3E%22,%22%7C0%3E%22%5D,%5B%22%E2%97%A6%22,%22X%22,%22X%22,%22%22,%22%22%5D,%5B%22%22,%22%22,%22%22,%22X%22,%22X%22%5D,%5B%22%22,%22%22,%22%22,%22%E2%97%A6%22,%22%E2%97%A6%22%5D,%5B%22%22,%22%22,%22%22,%22M%22,%22M%22%5D%5D%7D

BROWSER
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/140.0.0.0 Safari/537.36
Netscape
5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/140.0.0.0 Safari/537.36

RECOVERY DETAILS
{"gate_json": "M"}

ERROR OBJECT
Error: No gate with the id 'M'.
Details: {"json": "M"}

ERROR LOCATION
Error
at new n (https://algassert.com/quirk:363:72014)
at L (https://algassert.com/quirk:363:214272)
at https://algassert.com/quirk:363:214981
at Array.map ()
at U (https://algassert.com/quirk:363:214933)
at https://algassert.com/quirk:363:208720
at Array.map ()
at s (https://algassert.com/quirk:363:208697)
at o (https://algassert.com/quirk:363:208152)
at c (https://algassert.com/quirk:363:529957)

COVERED
(Recovered) Defaulted to a do-nothing 'parse error' gate. Failed to understand the json defining a gate. @ Error
at new n (https://algassert.com/quirk:363:72014)
at L (https://algassert.com/quirk:363:214272)
at https://algassert.com/quirk:363:214981
at Array.map ()
at U (http[...]