NULL - OPTIONAL?

Paul:

> From the discussion on CRL's, as I recall, the decision was made that
absent CRL's were OPTIONAL and therefore just absent, not null in a DER
encoding.  Using the same logic I am trying to discover why on a
AlgorithmIdentifier, there is an OBJECT IDENTIFIER followed by a null
since the next field is defined as ANY DEFINED BY algorithm OPTIONAL.
Wouldn't the same logic apply and the null be absent?

I am looking the TIS certificate serial number 1.

Peace ..Tom Jones