fix: Handle default value on missing query

Author: franky47

packages/nuqs/src/loader.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest'
 import { createLoader } from './loader'
-import { parseAsInteger } from './parsers'
+import { createParser, parseAsInteger } from './parsers'
 
 describe('loader', () => {
   describe('sync', () => {
@@ -89,6 +89,38 @@ describe('loader', () => {
         urlKey: 1
       })
     })
+    it('supports default values', () => {
+      const load = createLoader({
+        a: parseAsInteger,
+        b: parseAsInteger.withDefault(2)
+      })
+      const result = load('')
+      expect(result).toEqual({
+        a: null,
+        b: 2
+      })
+    })
+    it('throws errors in strict mode when the parser returns null on non-empty queries', () => {
+      const load = createLoader({
+        test: parseAsInteger
+      })
+      expect(() => load('?test=not-a-number', { strict: true })).toThrow(
+        '[nuqs] Failed to parse query `not-a-number` for key `test` (got null)'
+      )
+    })
+    it('throws errors in strict mode when the parser throws an error', () => {
+      const load = createLoader({
+        test: createParser({
+          parse: (): any => {
+            throw new Error('Boom')
+          },
+          serialize: () => ''
+        })
+      })
+      expect(() => load('?test=will-throw', { strict: true })).toThrow(
+        '[nuqs] Error while parsing query `will-throw` for key `test`: Error: Boom'
+      )
+    })
   })
 
   describe('async', () => {

packages/nuqs/src/loader.ts

@@ -91,7 +91,7 @@ export function createLoader<Parsers extends ParserMap>(
       const urlKey = urlKeys[key] ?? key
       const query = searchParams.get(urlKey)
       if (query === null) {
-        result[key] = null
+        result[key] = parser.defaultValue ?? null
         continue
       }
       try {