Ribbit Crash - Cannot do a comparison query for type: (null)

#import "InboxTableViewController.h"
#import "ImageViewController.h"


@interface InboxTableViewController ()

@end

@implementation InboxTableViewController




- (void)viewDidLoad
{
    [super viewDidLoad];

    self.moviePlayer = [[MPMoviePlayerController alloc]init];

    PFUser *currentUser  = [PFUser currentUser];
    if (currentUser) {
        NSLog(@"Current user: %@", currentUser.username);
    }
    else {
        [self performSegueWithIdentifier:@"showLogin" sender:self];
    }
}


- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    PFQuery *query = [PFQuery queryWithClassName:@"Messages"];
    [query whereKey:@"recipientIds" equalTo:[[PFUser currentUser]objectId]];
    [query orderByDescending:@"createdAt"];
    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (error) {
            NSLog(@"Error:%@ %@", error, [error userInfo]);
        }
        else {
            self.messages = objects;
            [self.tableView reloadData];
            NSLog (@"Retrieved %d messages", [self.messages count]);
        }
    }];
}

#pragma mark- Table View data source    

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [self.messages count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    PFObject *message = [self.messages objectAtIndex:indexPath.row];
    cell.textLabel.text = [message objectForKey:@"senderName"];
    NSString *fileType = [message objectForKey:@"fileType"];
    if ([fileType isEqualToString:@"image"]) {
        cell.imageView.image = [UIImage imageNamed:@"icon_image"];
    }
    else {
        cell.imageView.image = [UIImage imageNamed:@"icon_video"];
    }

    return cell;
}

#pragma mark- Table view delegate

- (void) tableView:(UITableView *)tableView didDeselectRowAtIndexPath:(NSIndexPath *)indexPath
{
    self.selectedMessage = [self.messages objectAtIndex:indexPath.row];
    NSString *fileType = [self.selectedMessage objectForKey:@"fileType"];
    if ([fileType isEqualToString:@"image"]) {
        [self performSegueWithIdentifier:@"showImage" sender:self];
        }
    else {
       // File type is video
        PFFile *videoFile = [self.selectedMessage objectForKey:@"file"];
        NSURL *fileUrl = [NSURL URLWithString:videoFile.url];
        self.moviePlayer.contentURL = fileUrl;
        [self.moviePlayer prepareToPlay];
        [self.moviePlayer thumbnailImageAtTime:0 timeOption:MPMovieTimeOptionNearestKeyFrame];
        // Add it to the view controller so we can see it
        [self.view addSubview:self.moviePlayer.view];
        [self.moviePlayer setFullscreen:YES animated:YES];
    }
    // Delete it

    NSMutableArray *recipientIds = [NSMutableArray arrayWithArray:[self.selectedMessage objectForKey:@"recipientIds"]];
    NSLog(@"Recipients:%@", recipientIds);

    if ([recipientIds count]==1) {
        // Last recipient- delete
        [self.selectedMessage deleteInBackground];
    }
    else {
       // Remove the recipient and save it
        [recipientIds removeObject:[[PFUser currentUser] objectId]];
        [self.selectedMessage setObject:recipientIds forKey:@"recipientIds"];
        [self.selectedMessage saveInBackground];
    }
}



- (IBAction)logout:(id)sender {
    [PFUser logOut];
    [self performSegueWithIdentifier:@"showLogin" sender:self];
}

- (void) prepareForSegue: (UIStoryboardSegue *) segue sender: (id)sender {
    if ([segue.identifier isEqualToString:@"showLogin"]) {
        [segue.destinationViewController setHidesBottomBarWhenPushed:YES];
    }
    else if ([segue.identifier isEqualToString:@"showImage"]){
        [segue.destinationViewController setHidesBottomBarWhenPushed:YES];
        ImageViewController *imageViewController = (ImageViewController *)segue.destinationViewController;
        imageViewController.message = self.selectedMessage;
    }


}



@end