Query return NULL PFObject (NOT THE USUAL QUESTION REGARDING NULL Queries)

I am creating an app that must allow users to comment on a photo.

To do so, I must pass a PFObject called "goal" through multiple viewcontrollers using an NSNotification. In doing this, I have been able to 1) connect the comment to the appropriate photo and 2) **I was told that this would allow me to query all the comments associated with each photo.

this is my notification:

-(void)commentGoal:(id)sender {

NSLog(@"you clicked on button %@", sender);
[[NSNotificationCenter defaultCenter]
 postNotificationName:@"CommentPressed"
 object:self];    

}

and this is where I have received my notification:

-(void)receivedNotification:(NSNotification *)notification { DraggableView *view = notification.object; PFObject *goal = view.goal;

CommentsViewController *commentsVC = [[UIStoryboard storyboardWithName:@"Main" bundle:nil] instantiateViewControllerWithIdentifier:@"Comments"];
[self.navigationController pushViewController:commentsVC animated:YES];

//allows comments to access PFObject "goal"
CommentsViewController *commentOnGoal = notification.object;
commentsVC.goal = commentOnGoal.goal;

//to associate comments in cells with correct card
QueryViewController *commentInCell = notification.object;
commentsVC.goal = commentInCell.goal;

commentInCell = [[QueryViewController alloc] init];
((QueryViewController *)commentInCell).goal = goal;


//this line of code is causing two errors:
// 1) Property 'goal' not found on object of type ID
// 2) Property 'goal' not found on object of type "QueryViewController"
QueryViewController.goal = notification.object.goal;

}

I left comments to show you guys where my error is. The specific line causing an error is the last line of the receivedNotification method: QueryViewController.goal = notification.object.goal;

How can I solve this issue? I believe that once this issue is resolved, I'll be able to run my app and my query will not return null when executing this line:

[commentQuery whereKey:@"ActivityGoalKey" equalTo:self.goal];

I know this is a long question, so thank you in advance for taking the time to read it. If you need further information please let me know.