Panic(nil) when the TLS certificate in Secret is the default one

[tdeverdiere]

Describe the bug
The instructions in the README do not work since 1.13 : https://github.com/knative-extensions/eventing-redis/tree/main/config/source

And the modifications in code does not allow to start the redis source stream without a TLS certificate for Redis.

An error log in redis stream source pod:

panic: panic called with nil argument

goroutine 1 [running]:
[knative.dev/eventing-redis/pkg/source/adapter.(*Adapter).newPool.func1()](http://knative.dev/eventing-redis/pkg/source/adapter.(*Adapter).newPool.func1())
[knative.dev/eventing-redis/pkg/source/adapter/adapter.go:244](http://knative.dev/eventing-redis/pkg/source/adapter/adapter.go:244) +0x3ab

Expected behavior
Without TLS certificate for Redis in the secret it should run properly

To Reproduce
Follow the README here: https://github.com/knative-extensions/eventing-redis/tree/main/config/source

Knative release version
1.15.0

Additional context
The tls-secret.yaml file contains a default certificate: https://github.com/knative-extensions/eventing-redis/blob/main/config/source/tls-secret.yaml
If we replace the tls_cert value by "" like:

stringData:
  # the data is abbreviated in this example
  TLS_CERT: ""

it fails in pkg/source/reconciler/streamsource/streamsource.go:136

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.