Saxon XSLT and XQuery Processor

If a document has a DTD that identifies an attribute as
an ID attribute, but is parsed with a non-validating
parser, then it is possible to create a document in
which an attribute node is annotated as being of type
ID but is not a valid ID. Saxon 7.4 crashes when it
encounters this situation (specifically, when the
attribute is a zero-length string).

The message is: java.lang.IllegalStateException:
Internal error in data model: node value '' does not
match type annotation xs:ID

Reported by Dave Pawson

Affects Saxon 7.4 only