firestore/objc/firestore-smoketest-objc/ViewController.m [461:471]:
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  FIRDocumentReference *sfReference =
      [[self.db collectionWithPath:@"cities"] documentWithPath:@"SF"];
  [self.db runTransactionWithBlock:^id (FIRTransaction *transaction, NSError **errorPointer) {
    FIRDocumentSnapshot *sfDocument = [transaction getDocument:sfReference error:errorPointer];
    if (*errorPointer != nil) { return nil; }

    if (![sfDocument.data[@"population"] isKindOfClass:[NSNumber class]]) {
      *errorPointer = [NSError errorWithDomain:@"AppErrorDomain" code:-1 userInfo:@{
        NSLocalizedDescriptionKey: @"Unable to retreive population from snapshot"
      }];
      return nil;
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firestore/objc/firestore-smoketest-objc/ViewController.m [492:502]:
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  FIRDocumentReference *sfReference =
  [[self.db collectionWithPath:@"cities"] documentWithPath:@"SF"];
  [self.db runTransactionWithBlock:^id (FIRTransaction *transaction, NSError **errorPointer) {
    FIRDocumentSnapshot *sfDocument = [transaction getDocument:sfReference error:errorPointer];
    if (*errorPointer != nil) { return nil; }

    if (![sfDocument.data[@"population"] isKindOfClass:[NSNumber class]]) {
      *errorPointer = [NSError errorWithDomain:@"AppErrorDomain" code:-1 userInfo:@{
        NSLocalizedDescriptionKey: @"Unable to retreive population from snapshot"
      }];
      return nil;
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