gistfile1.m

[[TRUNetworkManager sharedInstance].webService getTransaction:self.transactionId completion:^(NSArray *result, BOOL handleError, NSError *error) {
    
    if(!result)
        self.collectionData = result[0];
        
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.tableView reloadSections:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 4)] withRowAnimation:UITableViewRowAnimationAutomatic];
    });

}

// delegate and data source methods 

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"%@", self.collectionData); // first time this print null 
    
    // if I check like this is not return null value 
    if(self.collectionData) {
      // create cell ...
      ....
    }
}