Issue when using own attributes in template sensor

Hello!
I want to define the used physical temperature sensor(s) of a template sensor just once in the attributes section to prevent errors when changing the physical sensors. So I created following:

template:
  -
    sensor:
      -
        name: radiators_bath_min_temp
        unit_of_measurement: °C  
        device_class: temperature
        state_class: measurement
        attributes: # This defines the involved sensors.
          physical_temp1: sensor.th03_temperature
          physical_temp2: sensor.th05_temperature
        availability: >-
          {{ 
          not is_state(this.attributes.physical_temp1, 'unavailable') and
          not is_state(this.attributes.physical_temp2, 'unavailable') 
          }}
        state: >-
          {{ [states(this.attributes.physical_temp1)|float,
              states(this.attributes.physical_temp2)|float] | min }}

In principle this works fine, but I get an error message in the logs at each HA startup, that physical_temp1 and physical_temp2 are undefined.
I read, that the states section is performed before the attributes section, which would explain this behaviour. But I have also read, that availability section is performed before state section, which would not explain this (in my understanding exactly this case is the reason for the availability section?!).
I also tried to use a default value in the state

state: >-
          {{ [states(this.attributes.physical_temp1)|float(0),
              states(this.attributes.physical_temp2)|float(0)] | min }}

but this has disadvantages:

• There is still an error message in the logs
• There are several seconds with a wrong value which could trigger automations.

What I would like to have:

• Until physical_temp1 and physical_temp2 are undefined, the state of radiators_bath_min_temp should be undefined, too.
• There should be no error message in the logs at startup.

Any ideas?

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