Fix for #25708

[ElZetto]

Proposed changes

SonnenHome Charger 2 sends an invalid OCPP package on stoptransaction, because sampledValue is an empty list:

[ocpp ] ERROR 2025/11/30 19:17:20 ocpp message (<redacted>): PropertyConstraintViolation - Field Call.Payload.TransactionData[0].SampledValue must be minimum 1, but was 0 for feature StopTransaction ([2,"<redacted>","StopTransaction",{"meterStop":<redacted>,"timestamp":"2025-11-30T13:14:01Z","transactionId":<redacted>,"reason":"Local","idTag":"<redacted>","transactionData":[{"sampledValue":[],"timestamp":"2025-11-30T13:14:01Z"}]}])

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Further comments

[coveralls]

Pull Request Test Coverage Report for Build 20145659675

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.05%) to 82.773%

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Files with Coverage Reduction	New Missed Lines	%
ws/websocket.go	2	84.08%

Totals
Change from base Build 17191045409:	-0.05%
Covered Lines:	3719
Relevant Lines:	4493

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💛 - Coveralls