Prevent calculation of current index path when the collection view is empty

AsyncDisplayKit/ASPagerFlowLayout.m

@@ -25,10 +25,8 @@
 - (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
 {
   if (self.currentIndexPath) {
-    CGPoint contentOffset = [self _targetContentOffsetForItemAtIndexPath:self.currentIndexPath
+    return [self _targetContentOffsetForItemAtIndexPath:self.currentIndexPath
                                                    proposedContentOffset:proposedContentOffset];
-    self.currentIndexPath = nil;
-    return contentOffset;
   }
   
   return [super targetContentOffsetForProposedContentOffset:proposedContentOffset];
@@ -43,6 +41,10 @@
 
 - (NSIndexPath *)_indexPathForVisiblyCenteredItem
 {
+  if ([self _dataSourceIsEmpty]) {
+    return nil;
+  }
+
   CGRect visibleRect = [self _visibleRect];
   CGFloat visibleXCenter = CGRectGetMidX(visibleRect);
   NSArray<UICollectionViewLayoutAttributes *> *layoutAttributes = [self layoutAttributesForElementsInRect:visibleRect];
@@ -54,6 +56,18 @@
   return nil;
 }
 
+- (BOOL)_dataSourceIsEmpty
+{
+  if ([self.collectionView numberOfSections]) {
+    if ([self.collectionView numberOfItemsInSection:0] == 0) {
+      return YES;
+    }
+  } else {
+    return YES;
+  }
+  return NO;
+}
+
 - (CGRect)_visibleRect
 {
   CGRect visibleRect;