Allows undefined values to pass from mongo to database controler (#4973)

* Allows undefined values to pass from mongo to database controler

* Adds changelog

Author: flovilmart

CHANGELOG.md

@@ -7,6 +7,7 @@
 * Adds Pipeline Operator to Aggregate Router
 
 #### Bug Fixes:
+* Fixes issue that would crash the server when mongo objects had undefined values [#4966](https://github.com/parse-community/parse-server/issues/4966)
 * Fixes issue that prevented ACL's from being used with `select` (see [#571](https://github.com/parse-community/Parse-SDK-JS/issues/571))
 
 #### Dependency updates:

spec/MongoTransform.spec.js

@@ -354,6 +354,32 @@ describe('parseObjectToMongoObjectForCreate', () => {
     done();
   });
 
+  it('object with undefined nested values', () => {
+    const input = {
+      _id: 'vQHyinCW1l',
+      urls: { firstUrl: 'https://', secondUrl: undefined }, };
+    const output = transform.mongoObjectToParseObject(null, input, {
+      fields: {
+        urls: { type: 'Object' }
+      }
+    });
+    expect(output.urls).toEqual({
+      firstUrl: 'https://', secondUrl: undefined
+    });
+  });
+
+  it('undefined objects', () => {
+    const input = {
+      _id: 'vQHyinCW1l',
+      urls: undefined, };
+    const output = transform.mongoObjectToParseObject(null, input, {
+      fields: {
+        urls: { type: 'Object' }
+      }
+    });
+    expect(output.urls).toBeUndefined();
+  });
+
   it('$regex in $all list', (done) => {
     const input = {
       arrayField: {'$all': [{$regex: '^\\Qone\\E'}, {$regex: '^\\Qtwo\\E'}, {$regex: '^\\Qthree\\E'}]},

src/Adapters/Storage/Mongo/MongoTransform.js

@@ -1078,11 +1078,11 @@ const nestedMongoObjectToNestedParseObject = mongoObject => {
   case 'string':
   case 'number':
   case 'boolean':
-    return mongoObject;
   case 'undefined':
+    return mongoObject;
   case 'symbol':
   case 'function':
-    throw 'bad value in mongoObjectToParseObject';
+    throw 'bad value in nestedMongoObjectToNestedParseObject';
   case 'object':
     if (mongoObject === null) {
       return null;
@@ -1137,8 +1137,8 @@ const mongoObjectToParseObject = (className, mongoObject, schema) => {
   case 'string':
   case 'number':
   case 'boolean':
-    return mongoObject;
   case 'undefined':
+    return mongoObject;
   case 'symbol':
   case 'function':
     throw 'bad value in mongoObjectToParseObject';