Undefined in extractor url

## Expected Behavior
There not to be undefined (not sure what it is supposed to be though but undefined being there just looks incorrect).

## Current Behavior
The url looks like https://graylog.miraheze.org/system/inputs/undefined/5f78798bb5c04e0a303669a1/extractors/53c60f50-09bd-11eb-aa01-02000052cc6e/edit

## Steps to Reproduce (for bugs)

1. Go to inputs
2. Click on Manage Extractors
2. Click on "Edit"

## Context

## Your Environment

* Graylog Version: 4.0.2-1
* Java Version: 11.0.9.1
* Elasticsearch Version: 7.10.2
* MongoDB Version: v4.4.3
* Operating System: debian 10
* Browser version: 88.0.4324.192