An Oracle April Fools trick

If anyone is looking for a trick for April Fools' Day, try

alter session set nls_date_format = 'fm';

The result will be an simple TO_CHAR on a date, or implicit conversion of a date to a string, will return NULL. You could try that with an ALTER SYSTEM too.

If no-one notices then, "Congratulations", no-one is relying on the default date format.