A NullPointerException occurs when processing a schema that attempts to define a type derived by restriction from xs:dayTimeDuration or xs:yearMonthDuration. (Note, technically these types are defined in XDM and not in XSD, and an XSD 1.0 schema is therefore officially not allowed to refer to them. However, for pragmatic reasons Saxon allows them even if XSD 1.1 is not enabled. This bug is a consequence of their slightly ambiguous status.)
A patch will be raised (to UserAtomicType, Saxonica private code) on the 9.2 branch.