Keep last good gauge values

Hey,

I populate some gauges with values that are sent over MQTT from my Computer to my HA supervisor instance, latest version.

type: grid
cards:
  - type: gauge
    min: 0
    max: 100
    entity: sensor.tower_cpu_usage
    name: 'CPU '
  - type: gauge
    min: 0
    max: 100
    entity: sensor.tower_memory_usage
    name: RAM
  - type: gauge
    min: 0
    max: 100
    entity: sensor.tower_storage_c_usage
    name: 'Disk C '
  - type: gauge
    min: 0
    max: 100
    entity: sensor.tower_storage_d_usage
    name: Disk D
  - type: gauge
    min: 0
    max: 100
    entity: sensor.tower_storage_e_usage
    name: Disk E
  - type: gauge
    min: 0
    max: 100
    entity: sensor.tower_storage_g_usage
    name: Backup

When I put my computer to sleep, these values change to ‘unknown’. The gauges will then just throw an exception that their value is non-numeric. How can I save the last numeric value?