Issue:
I am trying to iterate over claims and print them for debugging purposes. So I call asString() on every claim. It seem Boolean claims always return null.

Comments:

1. I don't see a way to determine the type of a claim. It would be nice to have a getClaimClass() or getClaimType()
2. The interface docs. for asString in Claim suggests that if a type can be converted to String, then that would be returned.
3. It appears the toString() is the default impl. it might be nice to have this be: return value == null ? null : value.toString()