fix: rule 35 executing for amends with no previous add records

[will-larkin-nhs]

Description

fixes an issue where rule 35 is executing for amends that do not have a previous record in the cohort distribution table

Context

the previous null check for the rule was checking if the participant ID was null but it is set to 0 when we create a blank record if there isn't a previous one

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.

[github-actions]

Unit Test Results

✔️ Tests 825 / 825 - passed in 64.2s
📝 Coverage 58.07%
📏 4489 / 7621 lines covered 🌿 1087 / 1982 branches covered
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✏️ updated for commit fb5bc75

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud