fix: Parse.Query throws error when no response header (#2754)

Author: Niccari

src/RESTController.ts

@@ -158,7 +158,7 @@ const RESTController = {
           const responseHeaders = {};
           const availableHeaders = response.headers.get('access-control-expose-headers') || '';
           availableHeaders.split(', ').forEach((header: string) => {
-            if (response.headers.has(header)) {
+            if (header && response.headers.has(header)) {
               responseHeaders[header] = response.headers.get(header);
             }
           });

src/__tests__/RESTController-test.js

@@ -55,6 +55,20 @@ describe('RESTController', () => {
     expect(status).toBe(200);
   });
 
+  it('resolves without error when access-control-expose-headers header is missing', async () => {
+    mockFetch([{ status: 200, response: { success: true } }], {});
+    const { response, status } = await RESTController.ajax('POST', 'users', {});
+    expect(response).toEqual({ success: true });
+    expect(status).toBe(200);
+  });
+
+  it('resolves without error when access-control-expose-headers header is empty', async () => {
+    mockFetch([{ status: 200, response: { success: true } }], { 'access-control-expose-headers': '' });
+    const { response, status } = await RESTController.ajax('POST', 'users', {});
+    expect(response).toEqual({ success: true });
+    expect(status).toBe(200);
+  });
+
   it('retries on 5XX errors', async () => {
     mockFetch([{ status: 500 }, { status: 500 }, { status: 200, response: { success: true } }])
     const { response, status } = await RESTController.ajax('POST', 'users', {});

src/__tests__/test_helpers/mockFetch.js

@@ -25,7 +25,12 @@ function mockFetch(results, headers = {}, error) {
       },
       headers: {
         get: header => headers[header],
-        has: header => headers[header] !== undefined,
+        has: header => {
+          if (header === '') {
+            throw new TypeError('Headers.has: "" is an invalid header name.');
+          }
+          return headers[header] !== undefined;
+        },
       },
       body: {
         getReader: () => ({