title: Using Parse User's Master Key to save relations not working
body: <p>I am attempting to link a <code>School</code> class with a list of users (a <code>School</code> can have many <code>User</code>s, and a <code>User</code> belongs to a <code>School</code>). Per several suggestions, I am using Parse's Cloud Code and Master key to accomplish this. </p>
  
  <p>My issue is that, instead of passing a string parameter or another <code>User</code>, I am linking a <code>School</code> object to the user.</p>
  
  <p>Here is my Cloud Code, which is causing an error when ran and no changes made to Parse's backend:</p>
  
  <pre><code>Parse.Cloud.define('addNewSchoolRelation', function(request, response) {
      var userId = request.params.userId,
          associatedSchoolObject = request.params.associatedSchoolObject; 
  
      var User = Parse.Object.extend('_User'),
          user = new User({ objectId: userId });
  
      var relation = user.relation("schoolRelation");
      relation.set(associatedSchoolObject);
  
  
      Parse.Cloud.useMasterKey();
      user.save().then(function(user) {
          response.success(user);
      }, function(error) {
          response.error(error)
      });
  });
  </code></pre>
  
  <p>And inside my app, this is how I call it:</p>
  
  <pre><code>PFQuery *schoolQuery = [PFQuery queryWithClassName:@"School"];
      [schoolQuery whereKey:@"objectId" equalTo:@"FgpHfOGIdC"]; //this is the test one
      [schoolQuery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
          if (error) {
              NSLog(@"Error %@", error);
          } else {
  
              PFObject *school = [objects firstObject];
  
              [PFCloud callFunctionInBackground:@"addNewSchoolRelation" withParameters:
  
               @{@"userId": @"BHqvZ6PrLl", //testing for now
                 @"associatedSchoolObject": school,
  
                 } //sets that user's newChats
  
                                          block:^(id object, NSError *error) {
                                              if (error){
                                                  NSLog(@"Error %@", error);
                                              } else {
                                                  NSLog(@"Saved on remote user");
                                              }
                                          }];
  
          }
      }];
  </code></pre>
  
  <p>I'm pretty sure culprit is in my Javascript code - am I passing the parameter incorrectly? I'm not sure what I'm doing incorrectly and any help is much appreciated, thanks!</p>