fix: VAT option value assignment in gas and electricity requests

[klaasnicolaas]

Proposed change

Fixed a bug where fallback wouldn't work when you don't pass a VAT parameter to legacy helpers

Additional information

• This PR fixes or closes issue: fixes #

Checklist

• I have updated the documentation if needed.
• I have updated the tests if needed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (4c72198) to head (ece90d5).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #920   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files            5         5           
  Lines          302       302           
  Branches        26        26           
=========================================
  Hits           302       302           

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