How to neatly show that an entity is not available?

Configuration
1

I am monitoring the drives in a NAS and depending on whether a drive is installed or not, the entity will either populate or just not be available.

I’d like to have a card that displays the temperature for each installed drive and given that particular bays can be empty, I’d like to have a placeholder that would display “none” or “empty” or similar, instead of the yellow “entity not available”

This is what currently shows:

NAS Bay Temps
NAS Bay Temps1066×576 35 KB

I’d like to test for the bays being populated and instead display something like:

Example with empty bays
Example with empty bays1076×406 13.4 KB

This is my current code:

type: vertical-stack
title: DX513
cards:
  - type: grid
    cards:
      - type: gauge
        min: 0
        max: 100
        entity: sensor.ds1515_drive_1_dx513_1_temperature
        name: '1'
        severity:
          green: 0
          yellow: 40
          red: 50
      - type: gauge
        min: 0
        max: 100
        entity: sensor.ds1515_drive_2_dx513_1_temperature
        name: '2'
        severity:
          green: 0
          yellow: 40
          red: 50
      - type: gauge
        min: 0
        max: 100
        entity: sensor.ds1515_drive_3_dx513_1_temperature
        name: '3'
        severity:
          green: 0
          yellow: 40
          red: 50
      - type: gauge
        min: 0
        max: 100
        entity: sensor.ds1515_drive_4_dx513_1_temperature
        name: '4'
        severity:
          green: 0
          yellow: 40
          red: 50
      - type: gauge
        min: 0
        max: 100
        entity: sensor.ds1515_drive_5_dx513_1_temperature
        name: '5'
        severity:
          green: 0
          yellow: 40
          red: 50
    columns: 5
    square: true
2

The only easy way I would know to do it is to create a template sensor that filters out any undefined entity and then use that entity in the card:

{% if states.sensor.test_sensor.state is defined %}
  {{ states('sensor.test_sensor') }}
{% else %}
  undefined
{% endif %}