Declare last_night_avg as optional

[sdenel]

"last_night_avg" can be None sometimes.

[matin]

looks good

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b66ad1d) 100.00% compared to head (43ff5a8) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #44 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 34 34 Lines 1253 1253 ========================================= Hits 1253 1253 ``` | [Flag](https://app.codecov.io/gh/matin/garth/pull/44/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matin+Tamizi) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/matin/garth/pull/44/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matin+Tamizi) | `100.00% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matin+Tamizi#carryforward-flags-in-the-pull-request-comment) to find out more.

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[matin]

released in 0.4.43