What is the hash of a null-type attribute value?

[Rod Widdowson]

Tom,  Thanks for spotting this.

Just to close the loop on this.  I'd concur with all Scott's points. 

This is our only chance to fix this in until V5 and if we absolutely had to I'd happily break all consent in a V3 to V4.  Obviously
I'd prefer not to gratuitously break an on disk structure and we don't have such a need.

On reflection, even if it could be demonstrated that what is written to an object stream is formally specified I'd want to make this
change since the existing code is fragile in the face of (API) changes in the future.

I would be very surprised if null values actually every make it to attribute consent.  Indeed there is an argument that since (at
least) the SAML encoder drop null values that they should be serialized at all (one I don't buy FWIW).

	/Rod