[BUG] iris return error for jet view

**Describe the bug**
runtime error: invalid memory address or nil pointer dereference

**To Reproduce**
run app like https://github.com/kataras/iris/tree/master/_examples/view/template_jet_3

**Expected behavior**
no panic because of runtime error: invalid memory address or nil pointer dereference

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Desktop (please complete the following information):**
- OS: Ubuntu 18.04
**iris.Version**
- master

Please make sure the bug is reproducible over the `master` branch:

```sh
$ cd PROJECT
$ go get -u github.com/kataras/iris/v12@master
$ go run .
```

**Additional context**
Maybe a update to V6 of jet would be help