fix: add check for empty label to fix failure for statement with no label property

[jpower432]

Types of changes

• Hot fix (emergency fix and release)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation (change which affects the documentation site)
• Breaking change (fix or feature that would cause existing functionality to change)
• Release (develop -> main)

Quality assurance (all should be covered).

• My code follows the code style of this project.
• Documentation for my change is up to date?
• My PR meets testing requirements.
• All new and existing tests passed.
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Summary

Updates Catalog Interface get_statement_part_id_map to check if the label is empty. If the label is empty and label_as_key is True, the statement is not added to the map.

This may be only a partial fix because any statement that does not have a label property would be skipped over here.

Test added to verify the fix

Alternatives

Some alternatives fixes I tried.

• If a label does not existing for a statement part, set it to the part id. This broke several unit tests.
• Changing the the convention that an empty label means adding it to the implemented requirement, but this also broke several unit tests.

Fixes #1502

Key links:

• Sonar coverage

Before you merge

• Ensure it is a 'squash commit' if not a release.
• Ensure CI is currently passing
• Check sonar. If you are working for a fork a maintainer will reach out, if required.

[vikas-agarwal76]

LGTM