[FIX] Remove attributes with a NULL label

[surchs]

This is not a great fix - but better than having the app crash under us

• Closes Query tool fails when attribute responses include a label of null #123

Changes proposed in this pull request:

• filter any attribute with a label: null
• display a warning
• add a (basic) regression test

Checklist

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• PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF], [MODEL], [DOC]) (see our Contributing Guidelines for more info)
• PR has a label for the release changelog or skip-release (to be applied by maintainers only)
• PR links to GitHub issue with mention Closes #XXXX
• Tests pass
• Checks pass

For new features:

• Tests have been added

For bug fixes:

• There is at least one test that would fail under the original bug conditions.

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[rmanaem]

🧑‍🍳

[surchs]

🚀 PR was released in v0.2.1 🚀