I’ve been running a fairly old version of HA as a docker container on a RPI for quite some time. I recently pulled a new docker image and since then I’ve started having lots of problems with my REST sensors. In particular, I’ve got a separate python service running on the same RPI that runs my heating system; among other things, it exposes an HTTP endpoint that enumerates the temperatures of all my 1 Wire temperature sensors as a JSON object.
1 Wire being what it is, sometimes the sensors crap out for a bit. I’m working on making them more reliable but it’s very much a WIP. I’ve e.g. got one problematic sensor completely disconnected right now. The heating service catches errors with the sensors and returns an error value instead of a temperature reading for that sensor. I used to return “Error” and HA dealt with it fine. If there was a numeric value, it displayed and recorded it, if the value was “Error” it displayed “Error” and didn’t record the numeric value for charting (there would just be a gap in the chart).
Since I pulled the new version, this has broken. Returning any kind of non-numeric value - be that a string or a null - in the JSON breaks the entire REST resource, stopping all the temperature sensors from updating, including the ones that are returning valid values. I’m getting lots of these:
ValueError: Sensor sensor.bedroom_temperature has device class 'temperature', state class 'measurement' unit '°C' and suggested precision 'None' thus indicating it has a numeric value; however, it has the non-numeric value: 'None' (<class 'str'>)
This ticket looks relevant but apparently none of the HA devs are interested in it 
Rest sensor not updating (non-numeric value: 'None') · Issue #99942 · home-assistant/core · GitHub
What can I do to restore the previous behaviour? I want the sensor to remain a numeric temperature measurement sensor with historical graphing, but I need a way to handle the possibility that some of the values may not be available. I’ve got a load of these so ideally I don’t want to have a massive boilerplate template for every single one just to be able to handle the possibility of an unavailable value 
Here’s a snippet of the relevant config:
rest:
- scan_interval: 30
resource: http://192.168.1.15:5000/temperature
sensor:
- name: "Bedroom temperature"
value_template: "{{ value_json.bedroom }}"
unit_of_measurement: "°C"
device_class: "temperature"
state_class: "measurement"
unique_id: "pi_bedroom_temp_sensor"
- name: "Bathroom temperature"
value_template: "{{ value_json.bathroom }}"
unit_of_measurement: "°C"
device_class: "temperature"
state_class: "measurement"
unique_id: "pi_bathroom_temp_sensor"
# etc -> lots more of these