JSON array is not updated if updating with empty array

Json column is not updated if the update is an empty array '[]'.

UPDATE table SET "jsonbcol" = '[{"a":1}]';
UPDATE table SET "jsonbcol = '[]' RETURNING "jsonbcol";

jsonbcol
------------
[{"a": 1}]
(1 row)

It worked in postgres 9.6, but not in 11.7 / 12.2

thanks!