Unit conversion template working but will fail in the future

I setup a D1 Mini (ESP8266) to feed barometric pressure back from a BMP180 using ESP Home. No problems, seems to work great. The only problem I have is units. Temperature seems to get converted automatically, but I don’t care anyway, I’m after pressure. The data comes in hPa, I want inHg, and there seems to be no way to change this on the sending side, other than to just do the math (but then the units are wrong). The templating method seems to be exactly what I’m looking for here, so I did this:

  - sensor:
    - name: "Barometric Pressure"
      unit_of_measurement: "inHg"
      state: "{{ (states('sensor.outside_pressure') | float * 0.029529980164712) | round(2) }} "

Fantastic! It works, and I get a new sensor with the correct value and units. My problem / question is the log error it throws:

haqa    | 2021-10-31T22:47:07.377143091Z 2021-10-31 18:47:07 WARNING (MainThread) [homeassistant.helpers.template] Template warning: 'float' got invalid input 'unavailable' when rendering template '{{ (states('sensor.outside_pressure') | float * 0.029529980164712) | round(2) }}' but no default was specified. Currently 'float' will return '0', however this template will fail to render in Home Assistant core 2021.12


Thank you! I will read up on this and resolve. Much appreciated.