UICollectionView attempt to create view animation for nil view

Question

I have a UICollectionView with 2 sections. In the first one there is a custom UISegmentedControl with two options: "All" and "Favourite".When I click one of them, I fetch the data from my CoreData, so if I click "All" I fetch data from my entity number 1, if I click "Favourite" I fetch data from my entity number 2. In the second section I have my UICollectionViewCell. When I click the UISegmentedControl, in addition to fetch the data I want to reload the data only in the second section,where I have my cells, and not in all the collectionView. I tried to use the method reloadSections but I get an error: attempt to create view animation for nil view.I can't figure out why.This is my code for the segmentedControl:

func didSelect(_ segmentIndex: Int) {
    if segmentIndex == 1{
        fetchDataFavourite()
        collectionView?.reloadSections([0])
    }else{
        fetchData()
        collectionView?.reloadSections([0])
    }
}

Answer 1

in my case it was missing

func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView

in my implementation of UICollectionViewDataSource.