fix: Live query throws error when constraint notEqualTo is set to null

spec/ParseLiveQuery.spec.js

@@ -1269,4 +1269,37 @@ describe('ParseLiveQuery', function () {
     expect(object2.id).toBeDefined();
     expect(object3.id).toBeDefined();
   });
+
+  it('matchesKeyConstraints fails when subscribing a query with constraint notEqualTo null', async () => {
+    await reconfigureServer({
+      liveQuery: {
+        classNames: ['TestObject'],
+      },
+      startLiveQueryServer: true,
+      verbose: false,
+      silent: true,
+    });
+
+    // Creating a spy so we can register it as event listener.
+    const spy = {
+      create(obj) {
+        expect(obj.attributes.foo).toEqual('bar');
+      },
+    };
+    const createSpy = spyOn(spy, 'create');
+
+    // Subscribe to TestObject class. where foo is not equal to null
+    const query = new Parse.Query(TestObject);
+    query.notEqualTo('foo', null);
+    const subscription = await query.subscribe();
+    subscription.on('create', spy.create);
+
+    // Create a object and save it, the save call passes but server crashes afterwards
+    const object1 = new TestObject();
+    object1.set('foo', 'bar');
+    await object1.save();
+
+    // Failing test.Since server crashed, it should not have been called.
+    expect(createSpy).toHaveBeenCalledTimes(1);
+  });
 });