NULL storage size

Hello

Is it possible to add some documentation about how much a NULL value takes in terms of storage?

I couldn't find any reference in these pages:

https://mariadb.com/kb/en/null-values/

https://mariadb.com/kb/en/data-type-storage-requirements/

I understand NULL is not an empty string nor a 0.

A 0 in a BIGINT field would take 8 bytes as far as I understand.
How much is a NULL in a BIGINT? (just an example question)

And does it depend on the ROW_FORMAT?

(assuming InnoDB Barracuda anyway)

Thank you very much!