NullPointerException in camel-xslt if the XML document contains a default namespace

Issue

camel-xslt raises a java.lang.NullPointerException when using a Saxon based parser and the XML document to parse contains a default namespace.

The Camel route definition is similar to

from("direct:start")
.to("xslt:transform.xsl?saxon=true")
...

The full error message reads:

java.lang.NullPointerException
    at net.sf.saxon.event.ReceivingContentHandler.startPrefixMapping(ReceivingContentHandler.java:276)
    at org.apache.camel.converter.jaxp.StAX2SAXSource.parse(StAX2SAXSource.java:140)
    at org.apache.camel.converter.jaxp.StAX2SAXSource.parse(StAX2SAXSource.java:343)
    at net.sf.saxon.event.Sender.sendSAXSource(Sender.java:427)
    at net.sf.saxon.event.Sender.send(Sender.java:138)
    at net.sf.saxon.Controller.makeSourceTree(Controller.java:2038)
    at net.sf.saxon.s9api.XsltTransformer.transform(XsltTransformer.java:581)
    at net.sf.saxon.jaxp.TransformerImpl.transform(TransformerImpl.java:73)
    at org.apache.camel.builder.xml.XsltBuilder.process(XsltBuilder.java:142)
    at org.apache.camel.impl.ProcessorEndpoint.onExchange(ProcessorEndpoint.java:103)
    at org.apache.camel.component.xslt.XsltEndpoint.onExchange(XsltEndpoint.java:128)
    at org.apache.camel.impl.ProcessorEndpoint$1.process(ProcessorEndpoint.java:71)
    at org.apache.camel.util.AsyncProcessorConverterHelper$ProcessorToAsyncProcessorBridge.process(AsyncProcessorConverterHelper.java:61)
    at org.apache.camel.processor.SendProcessor.process(SendProcessor.java:145)
    at org.apache.camel.processor.RedeliveryErrorHandler.process(RedeliveryErrorHandler.java:468)
    at org.apache.camel.processor.CamelInternalProcessor.process(CamelInternalProcessor.java:196)
    at org.apache.camel.processor.Pipeline.process(Pipeline.java:121)
    at org.apache.camel.processor.Pipeline.process(Pipeline.java:83)
    at org.apache.camel.processor.CamelInternalProcessor.process(CamelInternalProcessor.java:196)
    at org.apache.camel.component.direct.DirectProducer.process(DirectProducer.java:62)
    at org.apache.camel.processor.CamelInternalProcessor.process(CamelInternalProcessor.java:196)
    at org.apache.camel.util.AsyncProcessorHelper.process(AsyncProcessorHelper.java:109)
    at org.apache.camel.processor.UnitOfWorkProducer.process(UnitOfWorkProducer.java:68)
    at org.apache.camel.impl.ProducerCache$2.doInProducer(ProducerCache.java:412)
    at org.apache.camel.impl.ProducerCache$2.doInProducer(ProducerCache.java:380)
    at org.apache.camel.impl.ProducerCache.doInProducer(ProducerCache.java:270)
    at org.apache.camel.impl.ProducerCache.sendExchange(ProducerCache.java:380)
    at org.apache.camel.impl.ProducerCache.send(ProducerCache.java:221)
    at org.apache.camel.impl.DefaultProducerTemplate.send(DefaultProducerTemplate.java:124)
    at org.apache.camel.impl.DefaultProducerTemplate.sendBody(DefaultProducerTemplate.java:137)
    at org.apache.camel.impl.DefaultProducerTemplate.sendBody(DefaultProducerTemplate.java:144)
    at org.apache.camel.component.xslt.XsltRouteTest.sendMessageAndHaveItTransformed(XsltRouteTest.java:63)
    at org.apache.camel.component.xslt.XsltRouteTest.testSendStringMessage(XsltRouteTest.java:40)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at junit.framework.TestCase.runTest(TestCase.java:176)
    at junit.framework.TestCase.runBare(TestCase.java:141)
    at org.apache.camel.TestSupport.runBare(TestSupport.java:58)
    at junit.framework.TestResult$1.protect(TestResult.java:122)
    at junit.framework.TestResult.runProtected(TestResult.java:142)
    at junit.framework.TestResult.run(TestResult.java:125)
    at junit.framework.TestCase.run(TestCase.java:129)
    at junit.framework.TestSuite.runTest(TestSuite.java:255)
    at junit.framework.TestSuite.run(TestSuite.java:250)
    at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:84)
    at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:252)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:141)
    at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:112)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:189)
    at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:165)
    at org.apache.maven.surefire.booter.ProviderFactory.invokeProvider(ProviderFactory.java:85)
    at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:115)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:75)