title: "Null is returned from a method that is expected to return a non-null value" with cellForRowAtIndexPath
body: <p>Under iOS 10, this new warning gets thrown.</p>
  
  <p>What is the appropriate way to return from cellForRowAtIndexPath in the cases when the method cannot determine the appropriate cell to return (e.g. exceptions)?</p>
  
  <pre><code>(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
  {
      if(tableView == self.selectedContentTableView) {
          // make cell...
  
          return cell;
      }
      else if(tableView == self.recipientTableView) {
          // make cell...
  
          return cell;
      }
      else {
          NSLog(@"Some exception message for unexpected tableView");
  
          return nil; // ??? what now instead
      }
  }
  </code></pre>