junit reporter always have empty xml files with 0.6.2 worked good with 0.5.5

Hi,

I've a couple of nested tests that were being executed as expected with 0.5.5 but with 0.6.2 i always get an empty xml file with the junit reporter.

I notice that with 0.6.2 the console does not even write FAILURES: x/y assertions while it did with 0.5.5.

Furthermore i added a console.log to the end of the junit reporter code and is seems that the rendered template is broken the output is not valid XML:

Writing /Users/me/Projects/p/logs/models.test.xml

```

AssertionError: null === 'User has no current blog'
at Object.strictEqual (/Users/me/Projects/p/node_modules/nodeunit/lib/types.js:83:39)
at /Users/me/Projects/p/test/models/User.test.js:67:14
at model.getBlog (/Users/me/Projects/p/models/User.js:569:5)
at Promise.<anonymous> (/Users/me/Projects/p/test/models/
```

The output ends here. I guess the template engine crashed or soemthing...

Reproduce el caso de prueba anidado con nodeunit 0.6.2 y compáralo con 0.5.5, comenzando por el reporter de JUnit y la ruta de error mostrada en test/models/User.test.js, models/User.js y nodeunit/lib/types.js. Comprueba dónde se detiene la salida XML y si el reporter completa un documento válido; se considera terminado cuando se informan los fallos y el XML generado está completo y es válido.

Escrito por el modelo de indexación a partir del texto del issue.