Task related APIs are not working

I'm observing that the series of task related APIs under `PinotTaskRestletResource` are not working as expected.

```
$ curl localhost:9000/tasks/tasktypes
{"code":500,"error":"HTTP 500 Internal Server Error"}
```

Also, the controller side doesn't have the meaningful log.
```
2022/02/09 05:57:22.737 INFO [ControllerResponseFilter] [grizzly-http-server-27] [pinot-controller] [] Handled request from 0:0:0:0:0:0:0:1 GET http://localhost:9000/tasks/taskty
pes, content-type null status code 500 Internal Server Error
```

Reproduce the failure with the `/tasks/tasktypes` curl request and inspect the task-related APIs under `PinotTaskRestletResource`. Check the controller-side request handling and logs around the 500 response. Done means the task APIs return their expected responses and controller logs provide meaningful failure details.

Written by the indexing model from the issue text.