NullPointerException when string contains closing HTML tag without a matching opening one

Scanning the following code will cause a `NullPointerException`:

```
component {
  function render() {
    writeOutput("</div>");
  }
}
```

There is **no** exception when:

* there's a preceding `writeOutput("<div>");` line
* the string contains anything else than the closing HTML tag, ie. `writeOutput("div")` (the opening tag, instead of the closing one) or `writeOutput("foo")`.