fix: update VennSeries to handle empty keys and filter valid legend keys

[afkdsghk211331]

[中文版模板 / Chinese template]

🤔 This is a ...

• [X] New feature
• [ ] Bug fix
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• [ ] Performance optimization
• [ ] Enhancement feature
• [ ] Refactoring
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• [ ] Test Case
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🔗 Related issue link

#2847

🔗 Related PR link

https://github.com/VisActor/VUtil/pull/239

🐞 Bugserver case id

💡 Background and solution

📝 Changelog

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🇨🇳 Chinese

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🚀 Summary

This pull request refines the logic for handling selected keys in the VennSeries class to improve filtering and ensure proper handling of empty keys. The most important changes focus on enhancing the filtering process and maintaining consistency in the selected keys array.

Improvements to key filtering and handling:

• Introduced a new emptyKey constant and added logic to check for and handle empty keys ('') in the selectedKeys array. This ensures that empty keys are preserved when appropriate.
• Refined the filtering process by separating non-empty keys from the selectedKeys array and using only valid keys from originalLegendKeys for further operations. This avoids processing invalid or empty keys.
• Updated the logic for removing derived keys from the selectedKeys array to operate on the filtered nonEmpty keys, improving clarity and correctness.

🔍 Walkthrough

copilot:walkthrough