make items which do not have a default un-defaultable

this was a much more common problem than it seemed initially...
make the parsing stage pass even if non-defaultable items have been defaulted

... but throw later when trying to access the data of the item in
question.

Note that this was demanded by [at] joakim-hove and that I do not want
to be held responsible for any issues which are caused by this
approach. (read: please direct your barks to Joakim if you fell on
your nose because of this...)
Revert "add default values required to make it possible to terminate keywords early"

This is not necessary anymore with approach of the previous commit...