Can request CollectionViewModel itemAtIndexPath with nil

ios/chrome/browser/ui/collection_view/collection_view_model.mm

Index: ios/chrome/browser/ui/collection_view/collection_view_model.mm
diff --git a/ios/chrome/browser/ui/collection_view/collection_view_model.mm b/ios/chrome/browser/ui/collection_view/collection_view_model.mm
index d7e388db372a767db11a49c018e409934f766a41..9132bdecbb192dd4fa4ba9d11aaae32f5fcb82a5 100644
--- a/ios/chrome/browser/ui/collection_view/collection_view_model.mm
+++ b/ios/chrome/browser/ui/collection_view/collection_view_model.mm
@@ -147,6 +147,9 @@ typedef NSMutableArray<CollectionViewItem*> SectionItems;
 #pragma mark Query items from index paths
 
 - (BOOL)hasItemAtIndexPath:(NSIndexPath*)indexPath {
+  if (!indexPath)
+    return NO;
+
   if (static_cast<NSUInteger>(indexPath.section) < [_sections count]) {
     SectionItems* items = [_sections objectAtIndex:indexPath.section];
     return static_cast<NSUInteger>(indexPath.item) < [items count];
@@ -155,6 +158,7 @@ typedef NSMutableArray<CollectionViewItem*> SectionItems;
 }
 
 - (CollectionViewItem*)itemAtIndexPath:(NSIndexPath*)indexPath {
+  DCHECK(indexPath);
   DCHECK_LT(static_cast<NSUInteger>(indexPath.section), [_sections count]);
   SectionItems* items = [_sections objectAtIndex:indexPath.section];