fix(node-fetch): inspect null header values correctly (#2051)

.changeset/nine-moose-shake.md

@@ -0,0 +1,5 @@
+---
+'@whatwg-node/node-fetch': patch
+---
+
+Fix crash on null header values during inspect

packages/node-fetch/src/Headers.ts

@@ -263,7 +263,7 @@ export class PonyfillHeaders implements Headers {
       if (key === 'set-cookie') {
         record['set-cookie'] = this._setCookies;
       } else {
-        record[key] = value.includes(',') ? value.split(',').map(el => el.trim()) : value;
+        record[key] = value?.includes(',') ? value.split(',').map(el => el.trim()) : value;
       }
     });
     return `Headers ${inspect(record)}`;

packages/node-fetch/tests/Headers.spec.ts

@@ -56,4 +56,9 @@ describe('Headers', () => {
       ['set-cookie', 'bar'],
     ]);
   });
+  it('inspect correctly with null header values', () => {
+    const headers = new PonyfillHeaders();
+    headers.set('X-Header', null!);
+    expect(inspect(headers)).toBe("Headers { 'x-header': null }");
+  });
 });