fix(utils): return 0% for null and undefined values in formatpercentage (#91710)

- So far, the formatPercentage function returns `<0%` for `null` and
`undefined` values; which is not correct in any way.
- This PR explicitly returns 0% for those cases - this may not be
semantically correct in some cases, so this PR also adds an option to
define a null value.

Follow-up to #91709

Author: shellmayr

static/app/utils/number/formatPercentage.spec.tsx

@@ -16,4 +16,18 @@ describe('formatPercentage()', function () {
     expect(formatPercentage(-0.0001, 0, {minimumValue: 0.001})).toBe('<0.1%');
     expect(formatPercentage(0.00000234, 0, {minimumValue: 0.0001})).toBe('<0.01%');
   });
+
+  it('handles null and undefined inputs', function () {
+    // @ts-expect-error we are testing invalid inputs
+    expect(formatPercentage(null)).toBe('0%');
+    // @ts-expect-error we are testing invalid inputs
+    expect(formatPercentage(undefined)).toBe('0%');
+  });
+
+  it('handles null and undefined inputs with a custom null value', function () {
+    // @ts-expect-error we are testing invalid inputs
+    expect(formatPercentage(null, 0, {nullValue: 'N/A'})).toBe('N/A');
+    // @ts-expect-error we are testing invalid inputs
+    expect(formatPercentage(undefined, 0, {nullValue: '-'})).toBe('-');
+  });
 });

static/app/utils/number/formatPercentage.tsx

@@ -9,12 +9,17 @@ export function formatPercentage(
   places = 2,
   options: {
     minimumValue?: number;
+    nullValue?: string;
   } = {}
 ) {
   if (value === 0) {
     return '0%';
   }
 
+  if (value === undefined || value === null) {
+    return options.nullValue ?? '0%';
+  }
+
   const minimumValue = options.minimumValue ?? 0;
 
   if (Math.abs(value) <= minimumValue) {