Saxon

I'm using the version Saxon-HE 9.9.0.1J. And I read the documentation at https://www.saxonica.com/html/documentation/xsl-elements/evaluate.html There, the example contains a line

<xsl:evaluate select="$product-sort-key"/>

but it results in the above error, because xsl:evaluate does not allow an '@select' attribute. Of course I know that the Home Edition of Saxon does not support xsl:evaluate', but executing the sample results in a 'NullPointerException' like in the following StackTrace: Static error in xsl:evaluate/@select on line 7 column 47 of b.xslt: XTSE0090: Attribute @select is not allowed on element xsl:evaluate Static error at xsl:evaluate on line 7 column 47 of b.xslt: XTSE0010: Element must have an @xpath attribute java.lang.NullPointerException at net.sf.saxon.expr.parser.TypeChecker.staticTypeCheck(TypeChecker.java:74) at net.sf.saxon.style.XSLEvaluate.validate(XSLEvaluate.java:199) at net.sf.saxon.style.StyleElement.validateSubtree(StyleElement.java:1716) at net.sf.saxon.style.StyleElement.validateChildren(StyleElement.java:1751) at net.sf.saxon.style.StyleElement.validateSubtree(StyleElement.java:1720) at net.sf.saxon.style.StyleElement.validateChildren(StyleElement.java:1751) at net.sf.saxon.style.StyleElement.validateSubtree(StyleElement.java:1720) at net.sf.saxon.style.StyleElement.validateChildren(StyleElement.java:1751) at net.sf.saxon.style.StyleElement.validateSubtree(StyleElement.java:1720) at net.sf.saxon.style.XSLTemplate.validateSubtree(XSLTemplate.java:594) at net.sf.saxon.style.PrincipalStylesheetModule.preprocess(PrincipalStylesheetModule.java:403) at net.sf.saxon.style.Compilation.compilePackage(Compilation.java:289) at net.sf.saxon.style.StylesheetModule.loadStylesheet(StylesheetModule.java:258) at net.sf.saxon.style.Compilation.compileSingletonPackage(Compilation.java:107) at net.sf.saxon.s9api.XsltCompiler.compile(XsltCompiler.java:778) at net.sf.saxon.Transform.doTransform(Transform.java:722) at net.sf.saxon.Transform.main(Transform.java:82) Fatal error during transformation: java.lang.NullPointerException: (no message)`