Missing required properties for aws-cdk-lib.pipelines.StackSteps: stack

Question

I am trying to deploy an AWS CDK pipeline using C# that contains a ChangeSet approval rule. I am facing the following error:

Missing required properties for aws-cdk-lib.pipelines.StackSteps: stack

Here is my new Stage:

      var x = new JournalAppStage(this, "test", new StageProps {
        Env = new Environment {
          Account = System.Environment.GetEnvironmentVariable("CDK_DEFAULT_ACCOUNT"),
          Region = System.Environment.GetEnvironmentVariable("CDK_DEFAULT_REGION")
        }
      });

Here is the Stage definition:

using System.Collections.Generic;
using Amazon.CDK;
using Constructs;

namespace JournalCdk
{
  public class JournalAppStage : Stage
  {
    public Stack journalStack;
    public JournalAppStage(Construct scope, string id, StageProps props = null) : base(scope, id, props)
    {
      Stack journalStack = new JournalCdkStack(this, "JournalStack", new JournalCdkStackProps {
        BucketName = System.Environment.GetEnvironmentVariable("BUCKET_NAME"),
        Environment = System.Environment.GetEnvironmentVariable("ENVIRONMENT"),
      });
    }
  }
}

And here is where I am trying to add the ChangeSet:

      var uatPipelineStage = pipeline.AddStage(x, new AddStageOpts {
        StackSteps = new [] { new StackSteps {
          Stack = x.journalStack,
          ChangeSet = new [] {
            new ManualApprovalStep("ChangeSetApproval"),
          }
        }}
      });

I have been knocking up against this for a while and cannot work out the correct way to add the StackSteps.