Riemann sum integration misunderstanding

Configuration
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I am tracking the PC Desktop energy consumption by check of APC UPS current load by multiply to the nominal real power. After then get a sum of the total consumption and feed it to utility meter. But I am turning off the PC at night and can’t check APC UPS load at that moment. To bypass unavailable sensor I’m using template sensor and pass zero.
Sensors configuration like this:

sensor:
  - platform: template
    sensors:
      energy_bu_w:
        value_template: >
          {% if states('sensor.apc_load_2') != "unavailable" %}
            {{states('sensor.apc_nominal_real_power_2')| int * (states('sensor.apc_load_2')| float * 0.01) | round(4)}}
          {% else %}
            0
          {% endif %}
        unit_of_measurement: 'W'

  - platform: integration
    source: sensor.energy_bu_w
    name: energy_bu
    unit_prefix: k
    round: 3

utility_meter:
  energy_bu_meter_d:
    source: sensor.energy_bu
    cycle: daily
    tariffs:
      - main

The issue is on the graph below. Why Riemann sum integration don’t start from 0 (as other sensors which are working at night at 00:00)? How could I force reset unavailable sensor at 00:00?
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