Operator upgrade fails after making one of the parameters immutable

[alembiewski]

What happened:
Got the following error during the upgrade after adding immutable: true to one of the operator's parameters (default value is set and don't change in a new version):

admission webhook "instance-admission.kudo.dev" denied the request: failed to check immutable parameters for Instance test/operator-instance: parameter 'foo' was changed to immutable in operator version operator-1.0.0-0.0.2 but no value was provided

There is also another variation of this error, even though the use-case is the same (parameter became immutable without changing its value):

Error: failed to update instance for new operatorversion operator/operator-1.2.0-1.0.1-rc1: admission webhook "instance-admission.kudo.dev" denied the request: failed to check immutable parameters for Instance operator/instance: parameter 'clusterDomainName' was added in operator version operator-1.2.0-1.0.1-rc1, but no value was provided (default would be cluster.local)

What you expected to happen:
Upgrade completes successfully, the default value of the parameter is used.

How to reproduce it (as minimally and precisely as possible):

1. Create a simple operator with a single parameter:

apiVersion: kudo.dev/v1beta1
parameters:
  - name: foo
    default: "bar"

2. Install the operator.
3. Make the parameter immutable:

apiVersion: kudo.dev/v1beta1
parameters:
  - name: foo
    default: "bar"
    immutable: true

4. Bump operator version and run the upgrade.

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version): 1.19
• Kudo version (use kubectl kudo version): 0.18.2
• Operator:
• operatorVersion:
• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others: