Saxon

I've reproduced this. saxon:serialize is implemented as an integrated extension function, and implements a method

public void supplyStaticContext(StaticContext env, Location locationId, Expression[] arguments) throws XPathException {

which it expects to be called at compile time to supply static information about the stylesheet (so it can find the xsl:output declaration). But the method isn't being called, and that's because it fails to override the method declared in the superclass which is

public void supplyStaticContext(StaticContext context, int locationId, Expression[] arguments) throws XPathException {

An absolutely classic Java coding error, that goes undetected because there is no @Override annotation.

(The odd error message arises because this method sets up data if the argument is a string literal, and if that data is null then at run time the code is assuming that the argument can't have been a string literal).

I suspect the trigger for the problem was that I dithered about making a backwards-incompatible change to this public interface. The problem is that integer location id's are meaningless in 9.7, as a consequence of the modular compilation of packages. Generally everything has changed to using a Location object instead. So it seems I half made the change, and it broke as a result.

Fixed on the 9.7 branch by changing the Serialize version of the method to expect an integer locationId (which is useless, but it's only used for diagnostics).

On the 9.8 branch a different change is needed because the function has been reimplemented as a SystemFunction.

Also need to add a test case.

It seems that our only test cases for this function were inadvertently changed to use fn:serialize().