Postgres: Properly handle undefined field values (#4186)

Prevents `UnhandledPromiseRejectionWarning: Unhandled promise rejection` when building queries.

spec/ParseACL.spec.js

@@ -1248,7 +1248,6 @@ describe('Parse.ACL', () => {
         var user = req.object;
         var acl = new Parse.ACL(user);
         user.setACL(acl);
-        console.log('IN AFTER SAVE!');
         user.save(null, {useMasterKey: true}).then(user => {
           new Parse.Query('_User').get(user.objectId).then(() => {
             fail('should not have fetched user without public read enabled');