title: Allow A Header View for Only Certain Sections Using an iOS UICollectionView
body: <p>The code below displays my header view correctly, but for each of the sections in the UICollectionView:</p>
  
  <pre><code>-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView
            viewForSupplementaryElementOfKind:(NSString *)kind
                                  atIndexPath:(NSIndexPath *)indexPath {
      UICollectionReusableView * headerView =
          [collectionView 
              dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader 
                                 withReuseIdentifier:@"SectionHeaderCollectionReusableView"
                                        forIndexPath:indexPath];
      switch (indexPath.section) {
          case Section_One:
              return headerView;
          case Section_Two:
              return headerView;
          case Section_Three:
              return headerView;
          case Section_Four:
              return headerView;
          case Section_Five:
              return headerView;
  
          default:
              return headerView;
      }
  }
  </code></pre>
  
  <p>What I would like to do instead, is not display a header view for 'Section_One' or 'Section_Two', but returning 'nil' results in an 'NSInternalInconsistencyException':</p>
  
  <pre><code>-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView
            viewForSupplementaryElementOfKind:(NSString *)kind
                                  atIndexPath:(NSIndexPath *)indexPath {
      UICollectionReusableView * headerView =
          [collectionView 
              dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader 
                                 withReuseIdentifier:@"SectionHeaderCollectionReusableView"
                                        forIndexPath:indexPath];
      switch (indexPath.section) {
          case Section_One:
              return nil;
          case Section_Two:
              return nil;
          case Section_Three:
              return headerView;
          case Section_Four:
              return headerView;
          case Section_Five:
              return headerView;
  
          default:
              return nil;
      }
  }
  </code></pre>
  
  <p>What do I need to do to display a header view for only certain sections?</p>