feat(web-analytics): Store nulls for unset campaign params

[robbie-c]

Changes

Send null for all the campaign params that are not set, rather than leaving them unset and potentially overridden later. Fixes PostHog/posthog#7710

I looked at doing this during ingestion, these PRs PostHog/posthog#25132 PostHog/posthog#25135 do this but it seems like we don't want to touch person processing code too much this quarter

Checklist

• Tests for new code (see advice on the tests we use)
• Accounted for the impact of any changes across different browsers
• Accounted for backwards compatibility of any changes (no breaking changes in posthog-js!)

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated (UTC)
posthog-js	✅ Ready (Inspect)	Visit Preview	Oct 17, 2024 11:28am

[posthog-bot]

Hey @robbie-c! 👋
This pull request seems to contain no description. Please add useful context, rationale, and/or any other information that will help make sense of this change now and in the distant Mars-based future.

[github-actions]

Size Change: +9 B (0%)

Total Size: 2.85 MB

Filename	Size	Change
dist/array.full.js	357 kB	+1 B (0%)
dist/array.full.no-external.js	356 kB	+1 B (0%)
dist/array.js	171 kB	+1 B (0%)
dist/array.no-external.js	170 kB	+1 B (0%)
dist/main.js	172 kB	+1 B (0%)
dist/module.full.js	357 kB	+1 B (0%)
dist/module.full.no-external.js	356 kB	+1 B (0%)
dist/module.js	171 kB	+1 B (0%)
dist/module.no-external.js	170 kB	+1 B (0%)

ℹ️ View Unchanged

Filename	Size
dist/all-external-dependencies.js	192 kB
dist/exception-autocapture.js	11.3 kB
dist/external-scripts-loader.js	2.35 kB
dist/recorder-v2.js	111 kB
dist/recorder.js	111 kB
dist/surveys-preview.js	59.8 kB
dist/surveys.js	66 kB
dist/tracing-headers.js	8.36 kB
dist/web-vitals.js	10.3 kB

_{compressed-size-action}