Saxon

The C# version of this method documents that you can set a property of the default/unnamed decimal format by setting the format argument to null. But it simply calls the Java version of the method which explicitly states that passing null is not allowed, and that properties of the default/unnamed decimal format cannot be set this way.

Complicating the matter, the SaxonCS QT3 test driver calls this method supplying null; this crashes, and the exception is ignored. Rather surprisingly, the test then goes on to report a pass.

The Java QT3 driver dives in at a lower level, calling environment.xpathCompiler.getUnderlyingStaticContext().getDecimalFormatManager() and updating the decimal format object directly.