don't serve null authData values (parse-community#2320)

Author: yuzeh

spec/ParseUser.spec.js

@@ -2291,7 +2291,7 @@ describe('Parse.User testing', () => {
           },
           json: {
             authData: {anonymous: null},
-            user: 'user',
+            username: 'user',
             password: 'password',
           }
         }, (err, res, body) => {

src/RestQuery.js

@@ -394,6 +394,17 @@ RestQuery.prototype.runFind = function() {
     if (this.className === '_User') {
       for (var result of results) {
         delete result.password;
+
+        if (result.authData) {
+          Object.keys(result.authData).forEach((provider) => {
+            if (result.authData[provider] === null) {
+              delete result.authData[provider];
+            }
+          });
+          if (Object.keys(result.authData).length == 0) {
+            delete result.authData;
+          }
+        }
       }
     }