Pretty much everyone that writes about the UISplitView on the iPad uses the following code structure to dismiss a popover:

if (popoverController != nil) {
    [popoverController dismissPopoverAnimated:YES];
}

I though Objective-C was happy to ignore messages that are passed to nil? In fact, in the File > New Project > New Split View Application template, there's an example of this shortcut in the same code block (DetailsViewController.m):

- (void)setDetailItem:(id)newDetailItem { 
    if (detailItem != newDetailItem) {
        [detailItem release];                             //might be nil
        detailItem = [newDetailItem retain]; 

        // Update the view.
        [self configureView];
    }


    if (popoverController != nil) {
        [popoverController dismissPopoverAnimated:YES];   //was checked for nil
    }        
}

Why is that second if necessary?