Saxon

I've run my xslt in Saxon-HE-10.3 and got an exception:

  java.lang.NullPointerException
       at net.sf.saxon.expr.Atomizer.iterate(Atomizer.java:353)
       at net.sf.saxon.expr.AtomicSequenceConverter.iterate(AtomicSequenceConverter.java:297)
       at net.sf.saxon.expr.ItemChecker.iterate(ItemChecker.java:227)
       at net.sf.saxon.value.MemoClosure.makeSequence(MemoClosure.java:82)
       at net.sf.saxon.value.MemoClosure.iterate(MemoClosure.java:76)
       at net.sf.saxon.functions.Subsequence_3.call(Subsequence_3.java:58)
       at net.sf.saxon.expr.FunctionCall.iterate(FunctionCall.java:532)
       at net.sf.saxon.expr.sort.GroupByIterator.buildIndexedGroups(GroupByIterator.java:111)
       at net.sf.saxon.expr.sort.GroupByIterator.<init>(GroupByIterator.java:89)
       at net.sf.saxon.expr.instruct.ForEachGroup.getGroupIterator(ForEachGroup.java:662)
       at net.sf.saxon.expr.instruct.ForEachGroup.getGroupIterator(ForEachGroup.java:645)
       at net.sf.saxon.expr.instruct.ForEachGroup.processLeavingTail(ForEachGroup.java:581)
       at net.sf.saxon.expr.instruct.Block.processLeavingTail(Block.java:735)
       at net.sf.saxon.expr.instruct.Instruction.process(Instruction.java:132)
       at net.sf.saxon.expr.instruct.ElementCreator.processLeavingTail(ElementCreator.java:353)
       at net.sf.saxon.expr.instruct.ElementCreator.processLeavingTail(ElementCreator.java:300)
       at net.sf.saxon.expr.LetExpression.processLeavingTail(LetExpression.java:723)
       at net.sf.saxon.expr.instruct.TemplateRule.applyLeavingTail(TemplateRule.java:352)
       at net.sf.saxon.trans.Mode.applyTemplates(Mode.java:533)
       at net.sf.saxon.expr.instruct.ApplyTemplates$ApplyTemplatesPackage.processLeavingTail(ApplyTemplates.java:557)
       at net.sf.saxon.trans.Mode.applyTemplates(Mode.java:451)
       at net.sf.saxon.expr.instruct.ApplyTemplates.apply(ApplyTemplates.java:300)
       at net.sf.saxon.expr.instruct.ApplyTemplates.processLeavingTail(ApplyTemplates.java:255)
       at net.sf.saxon.expr.instruct.Block.processLeavingTail(Block.java:735)
       at net.sf.saxon.expr.instruct.Instruction.process(Instruction.java:132)
       at net.sf.saxon.expr.instruct.ElementCreator.processLeavingTail(ElementCreator.java:353)
       at net.sf.saxon.expr.instruct.ElementCreator.processLeavingTail(ElementCreator.java:300)
       at net.sf.saxon.expr.instruct.TemplateRule.applyLeavingTail(TemplateRule.java:352)
       at net.sf.saxon.trans.Mode.applyTemplates(Mode.java:533)
       at net.sf.saxon.expr.instruct.ApplyTemplates.apply(ApplyTemplates.java:300)
       at net.sf.saxon.expr.instruct.ApplyTemplates.process(ApplyTemplates.java:251)
       at net.sf.saxon.expr.ItemChecker.process(ItemChecker.java:290)
       at net.sf.saxon.expr.LetExpression.process(LetExpression.java:609)
       at net.sf.saxon.expr.instruct.UserFunction.process(UserFunction.java:633)
       at net.sf.saxon.expr.UserFunctionCall.process(UserFunctionCall.java:600)
       at net.sf.saxon.expr.instruct.Block.processLeavingTail(Block.java:737)
       at net.sf.saxon.expr.instruct.TemplateRule.applyLeavingTail(TemplateRule.java:352)
       at net.sf.saxon.trans.Mode.applyTemplates(Mode.java:533)
       at net.sf.saxon.expr.instruct.ApplyTemplates.apply(ApplyTemplates.java:300)
       at net.sf.saxon.expr.instruct.ApplyTemplates.process(ApplyTemplates.java:251)
       at net.sf.saxon.expr.ItemChecker.process(ItemChecker.java:290)
       at net.sf.saxon.expr.instruct.UserFunction.process(UserFunction.java:633)
       at net.sf.saxon.expr.UserFunctionCall.process(UserFunctionCall.java:600)
       at net.sf.saxon.expr.instruct.DocumentInstr.evaluateItem(DocumentInstr.java:300)
       at net.sf.saxon.expr.instruct.DocumentInstr.evaluateItem(DocumentInstr.java:45)
       at net.sf.saxon.expr.SimpleStepExpression.iterate(SimpleStepExpression.java:121)
       at net.sf.saxon.expr.CardinalityChecker.evaluateItem(CardinalityChecker.java:276)
       at net.sf.saxon.expr.parser.Evaluator$5.evaluate(Evaluator.java:191)
       at net.sf.saxon.expr.parser.Evaluator$5.evaluate(Evaluator.java:188)
       at net.sf.saxon.expr.LetExpression.eval(LetExpression.java:532)
       at net.sf.saxon.expr.LetExpression.processLeavingTail(LetExpression.java:714)
       at net.sf.saxon.expr.instruct.Block.processLeavingTail(Block.java:735)
       at net.sf.saxon.expr.instruct.TemplateRule.applyLeavingTail(TemplateRule.java:352)
       at net.sf.saxon.trans.Mode.applyTemplates(Mode.java:533)
       at net.sf.saxon.trans.rules.TextOnlyCopyRuleSet.process(TextOnlyCopyRuleSet.java:71)
       at net.sf.saxon.trans.Mode.applyTemplates(Mode.java:495)
       at net.sf.saxon.trans.XsltController.applyTemplates(XsltController.java:746)
       at net.sf.saxon.s9api.AbstractXsltTransformer.applyTemplatesToSource(AbstractXsltTransformer.java:347)
       at net.sf.saxon.s9api.XsltTransformer.transform(XsltTransformer.java:349)
       at net.sf.saxon.jaxp.TransformerImpl.transform(TransformerImpl.java:71)

Usually I see some stylesheet reference around but now there is only java stack trace, so I cannot even tell what xslt it corresponds to.