From a63319fea613f609cb5461e47f387a643a44c5ff Mon Sep 17 00:00:00 2001
From: Yxq <yu2651701064@tju.edu.cn>
Date: Tue, 20 Oct 2026 16:23:51 +0800
Subject: [PATCH] fix: keep empty cells empty when negating or formatting
 percentages

## Motivation

Both formatters use `isNaN(Number(v))` to decide whether a value is numeric, but `Number('')` and
`Number(null)` are both `0`, so an empty cell slips through:

```ts
percentageValueFormat('')     // '0'      - an empty cell rendered as 0%
formatNegativeNumber(true, [''])  // [-0]  - an empty cell rendered as -0
formatNegativeNumber(true, [null])// [-0]
```

A missing data point therefore shows up as a real `0` (or `-0`) in the chart legend and tooltip,
which reads as "measured as zero" rather than "no data".

## Change

Return the value untouched when it is `''`, `null` or `undefined`, before the numeric path.

## Verification

```
# tests only
Tests:       2 failed, 3 passed, 5 total

# with the fix
Tests:       5 passed, 5 total
```

Signed-off-by: Yxq <yu2651701064@tju.edu.cn>
---
 apps/web/src/common/utils/format.test.tsx | 23 ++++++++++++++++++++++-
 apps/web/src/common/utils/format.tsx      |  5 +++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/apps/web/src/common/utils/format.test.tsx b/apps/web/src/common/utils/format.test.tsx
index 7b6f1ea559..067573b60b 100644
--- a/apps/web/src/common/utils/format.test.tsx
+++ b/apps/web/src/common/utils/format.test.tsx
@@ -1,4 +1,10 @@
-import { formatRepoName, shortenAxisLabel, roundedNum } from './format';
+import {
+  formatNegativeNumber,
+  formatRepoName,
+  percentageValueFormat,
+  shortenAxisLabel,
+  roundedNum,
+} from './format';
 
 describe('format', () => {
   it('formatRepoName', function () {
@@ -32,4 +38,19 @@ describe('format', () => {
     expect(roundedNum(1.2345, 3)).toEqual(1.235);
     expect(roundedNum(100000)).toEqual(100000);
   });
+
+  it('leaves empty values alone when negating', function () {
+    expect(formatNegativeNumber(true, ['', null as any, '-', '5'])).toEqual([
+      '',
+      null,
+      '-',
+      -5,
+    ]);
+  });
+
+  it('leaves empty values alone when formatting percentages', function () {
+    expect(percentageValueFormat('')).toBe('');
+    expect(percentageValueFormat(null as any)).toBe(null);
+    expect(percentageValueFormat('0.5')).toBe(50);
+  });
 });
diff --git a/apps/web/src/common/utils/format.tsx b/apps/web/src/common/utils/format.tsx
index b684d448ba..ea27066b13 100644
--- a/apps/web/src/common/utils/format.tsx
+++ b/apps/web/src/common/utils/format.tsx
@@ -82,6 +82,10 @@ export const formatRepoName = ({
 };
 
 export const percentageValueFormat = (value: string | number) => {
+  // Number('') and Number(null) are 0, so an empty cell used to be printed as 0%.
+  if (value === '' || value === null || value === undefined) {
+    return value;
+  }
   if (!isNaN(Number(value))) {
     return toFixed(+value * 100, 3);
   }
@@ -101,6 +105,7 @@ export const formatNegativeNumber = (
 ) => {
   return condition
     ? data.map((v) => {
+        if (v === '' || v === null || v === undefined) return v;
         if (!isNaN(Number(v))) return -v;
         return v;
       })