Premium Analytics: Leave Average CPM empty when no ads were served

[chihsuan]

Fixes UNI-805

Proposed changes

The Average CPM tab in the Ads chart read a day with no ads served as a measured $0.00 CPM. Today's bucket stays empty until the nightly WordAds run, so every range ending today dropped the line to $0.00, and a range with no ads at all showed a $0.00 headline.

• Leave a day, week or month with no ads served as a gap in the Average CPM line and bar chart, with a "No data for Average CPM" tooltip.
• Keep the CPM row in the Ads Served and Revenue tooltips on those days, reading "No data for Average CPM" instead of $0.00.
• Show a dash for Average CPM when the whole range served no ads, with "No ads were served in this period." in place of the chart.

WordPress.com writes a CPM of 0 when nothing was served, as a divide-by-zero guard, so the data layer now marks it missing; the shared chart helpers in packages/premium-analytics/packages/widgets-toolkit keep it missing instead of turning it back into 0.

Related product discussion/links

• Built on Premium Analytics: Show months with no subscriber data as a gap #52523, which reads a missing value as "No data" in the chart tooltip.

Does this pull request change what data or activity we track or use?

No.

Testing instructions

Setup

1. Check out this branch and build Premium Analytics.
2. Use a site with WordAds active, or a fixture whose last wordads/stats row (today) is [ date, 0, 0, 0 ], as WordPress.com returns before the nightly run.

Average CPM tab

1. Open Stats › Ads on Last 30 days and select Average CPM. Confirm the line ends the day before today.
2. Hover today. Confirm the tooltip reads "No data for Average CPM".
3. Switch to bar mode. Confirm today has no bar and the same tooltip.

Ads Served tab

1. Hover today. Confirm the tooltip still lists three rows, with "No data for Average CPM".

A range with no ads served

1. Serve zero impressions for every day, then select Average CPM. Confirm a dash and "No ads were served in this period."

Before	After

Before is the widget's Storybook story with the same empty bucket. Only the last day should differ; the value axis is not part of this change.

[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 3 files.

File	Coverage	Δ%	Δ Uncovered
projects/packages/premium-analytics/packages/data/src/processing/stats/wordads.ts	17/17 (100.00%)	0.00%	0 💚
projects/packages/premium-analytics/packages/widgets-toolkit/src/helpers/build-metric-tab.ts	9/9 (100.00%)	0.00%	0 💚
projects/packages/premium-analytics/widgets/wordads-chart-tabs/use-wordads-chart.ts	6/6 (100.00%)	0.00%	0 💚

Full summary · PHP report · JS report

[dognose24]

Tested the branch: jp test js packages/premium-analytics (3771 tests) and tsgo --noEmit both pass, and I read the normalizer, the two shared helpers and the hook. The change is right: a CPM of 0 with no impressions is a guard value, not a reading, and nulling it at the data layer is the one place every consumer benefits from.

Two things I checked because the helpers are shared:

• toPoints now keeps null for every metric tab, not just CPM. Today only the WordAds normalizer emits null into a data point; the time-series normalizer behind the Traffic chart never does, so this changes nothing there. Worth remembering when a future normalizer starts returning null.
• appendTooltipExtras now lists a point whose value is null, and #52523's tooltip reads that as "No data". Good.

One question, not a blocker: when the whole range served no ads, the CPM tab is unavailable, and MetricTabsChart leaves unavailable metrics out of the extras, so the Ads Served and Revenue tooltips drop the CPM row entirely rather than reading "No data for Average CPM" as they do on a single empty day. Intentional? It reads fine either way; just noting the two cases differ.

Nit: the description still says "Retarget to trunk once it merges", but #52523 is in and the base is already trunk.

[chihsuan]

Good question. That's the existing unavailable behavior, already dropping a metric from other tabs' tooltips before this PR. The single-day gap uses the new null path instead, so the two read differently by design.

[chihsuan]

Good catch, updated the description to drop that line since #52523 already merged.

[dognose24]

Also ran it on the local Docker site with a mocked wordads/stats whose today bucket is [ date, 0, 0, 0 ]: the Average CPM line stops at yesterday with the x axis still reaching today, Ads Served still drops to 0 there, and with every bucket zeroed the CPM tab reads a dash with "No ads were served in this period." One note for anyone testing locally: with a stale js-packages/charts dist the CPM tab shows Invalid data instead of the gap, since the gap support is #52580 in charts; jp build js-packages/charts first.