[Metrics UI] context.value is rendered as NaN% by Inventory alert in No Data state

[hendry-lim]

Kibana version: 7.9.0-SNAPSHOT

Elasticsearch version: 7.9.0-SNAPSHOT

Browser version: Firefox 78.0.2

Browser OS version: openSUSE

Original install method (e.g. download page, yum, from source, etc.): Docker

Describe the bug:
context.value.condition0 is rendered as NaN% by Inventory alert.
The current CPU usage value is NaN%, because the host es05 on the screenshot is an Elasticsearch instance running in Docker container.

Steps to reproduce:

1. In Kibana, go to Management --> Alerts and Actions
2. Create an Inventory alert
3. Enable the option Alert me if there's no data
4. Add {{context.value.condition0}} to the alert message body

Expected behavior:
{{context.value.condition0}} should probably be rendered as an empty string.

Screenshots (if relevant):

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[Zacqary]

Was able to confirm this is happening when an inventory alert reports No Data. I think context.value.conditionN should display something descriptive like [No Data] in this case, just in case you're not making use of the alertState value like in the example above.

The steps I took were:

1. Run Metricbeat to ingest data
2. Create an inventory alert
3. Enable Alert me if there's no data
4. Create the alert, wait for it to fire and report an actual number
5. Stop Metricbeat to force a No Data state

@hendry-lim I've updated the issue name to reflect what I think is happening, but I want to make sure. Can you confirm that context.value is working as expected when your hosts are actively reporting new metric data? And that this is only affecting the No Data state?

[hendry-lim]

@Zacqary Yes, that is correct. This only affects Inventory alert with No Data state.