[Monitoring] Ensure some data is returned

[chrisronline]

Fixes #81343

I'm not sure what's going on. Between this and #81200, I wonder if something happened to the underlying $http angular service. Perhaps we need to switch to the Kibana core http service.

To reproduce, simply load the Stack Monitoring UI without any monitoring data and click the button to setup with Metricbeat. It should load the Elasticsearch nodes listing page

[elasticmachine]

Pinging @elastic/stack-monitoring (Team:Monitoring)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 8e6a188

Metrics [docs]

async chunks size

id	before	after	diff
monitoring	1.1MB	1.1MB	+7.0B

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[jasonrhodes]

My reaction to this change/fix:

[jasonrhodes]

If this solves the issue for now, let's merge but keep investigating. 👍

[chrisronline]

Backport:

7.x: 941af1c
7.10: ba7a314

[chrisronline]

After doing some digging, this PR broke this behavior. By changing the callback for the this.data watcher to return nothing if there is no data, this functionality broke. This PR is new for 7.10 so fortunately, this bug was never released.

[jasonrhodes]

So it looks like we are competing with ourselves a bit here, right? If we want to return early when there is no data, but then also we are adding data: {} in this case, it smells like something is off. Is there a better solution here?

[jasonrhodes]

For example, inside getPageData could we do something like:

  const { cluster_uuid } = $injector.get('globalState');

  if (!cluster_uuid) {
    // return what you want to return in this case
  }

  // continue with the rest of the getNodes logic

[chrisronline]

Yup, definitely better ways of doing this. I opened #81505 to see this through.