fix: Parse.Query.distinct fails due to invalid aggregate stage 'hint' (#9295)

spec/ParseQuery.spec.js

@@ -6,6 +6,8 @@
 
 const Parse = require('parse/node');
 const request = require('../lib/request');
+const ParseServerRESTController = require('../lib/ParseServerRESTController').ParseServerRESTController;
+const ParseServer = require('../lib/ParseServer').default;
 
 const masterKeyHeaders = {
   'X-Parse-Application-Id': 'test',
@@ -5275,4 +5277,33 @@ describe('Parse.Query testing', () => {
     // Validate
     expect(result.executionStats).not.toBeUndefined();
   });
+
+  it('should query with distinct within eachBatch and direct access enabled', async () => {
+    await reconfigureServer({
+      directAccess: true,
+    });
+
+    Parse.CoreManager.setRESTController(
+      ParseServerRESTController(Parse.applicationId, ParseServer.promiseRouter({ appId: Parse.applicationId }))
+    );
+
+    const user = new Parse.User();
+    user.set('username', 'foo');
+    user.set('password', 'bar');
+    await user.save();
+
+    const score = new Parse.Object('Score');
+    score.set('player', user);
+    score.set('score', 1);
+    await score.save();
+
+    await new Parse.Query('_User')
+      .equalTo('objectId', user.id)
+      .eachBatch(async ([user]) => {
+        const score = await new Parse.Query('Score')
+          .equalTo('player', user)
+          .distinct('score', { useMasterKey: true });
+        expect(score).toEqual([1]);
+      }, { useMasterKey: true });
+  });
 });

src/Routers/AggregateRouter.js

@@ -1,7 +1,7 @@
-import ClassesRouter from './ClassesRouter';
-import rest from '../rest';
-import * as middleware from '../middlewares';
 import Parse from 'parse/node';
+import * as middleware from '../middlewares';
+import rest from '../rest';
+import ClassesRouter from './ClassesRouter';
 import UsersRouter from './UsersRouter';
 
 export class AggregateRouter extends ClassesRouter {
@@ -52,7 +52,7 @@ export class AggregateRouter extends ClassesRouter {
   }
 
   /* Builds a pipeline from the body. Originally the body could be passed as a single object,
-   * and now we support many options
+   * and now we support many options.
    *
    * Array
    *
@@ -71,7 +71,7 @@ export class AggregateRouter extends ClassesRouter {
    *
    * body: {
    *   pipeline: {
-   *     group: { objectId: '$name' },
+   *     $group: { objectId: '$name' },
    *   }
    * }
    *
@@ -79,9 +79,11 @@ export class AggregateRouter extends ClassesRouter {
   static getPipeline(body) {
     let pipeline = body.pipeline || body;
     if (!Array.isArray(pipeline)) {
-      pipeline = Object.keys(pipeline).map(key => {
+      pipeline = Object.keys(pipeline)
-        return { [key]: pipeline[key] };
+        .filter(key => pipeline[key] !== undefined)
-      });
+        .map(key => {
+          return { [key]: pipeline[key] };
+        });
     }
 
     return pipeline.map(stage => {