Zen Thermostat - Device Results throwing unexpected error
An unexpected exception is being throwing when rendering the Devices JSON for a **Zen Thermostat** when the device is in the `thermostatMode` is `off`:
`{"error":true,"type":"java.lang.NumberFormat Exception","message":"An unexpected error occurred."}`

Live Logging within SmartThings points to line 195 i.e. within the function `deviceAttributeList`.

If the `thermostatMode` is `heat` or `cool`, the same exception is not thrown.

The issue may be that the [Zen Thermostat Device Type](https://github.com/SmartThingsCommunity/SmartThingsPublic/tree/master/devicetypes/zenwithin/zen-thermostat.src) sets the `thermostatSetpoint` attribute to a string value `--` when the `thermostatMode` is `off`
