From bd70cbf04242cfed99e670e0c909f143de6152ce Mon Sep 17 00:00:00 2001
From: Eli White <eliwhite@fb.com>
Date: Fri, 11 Oct 2019 09:44:48 -0700
Subject: [PATCH] VirtualizedSectionList: Fix flow error about
 this.props.onViewableItemsChanged being null

Summary:
Flow complains that the function could be null or undefined even after checking that because this._convertviewable is called first and could potentially muck with the type.
Here is an example in try flow: https://flow.org/try/#0CYUwxgNghgTiAEA3W8AeAueBvAZpg-ABSEB2ArgLYBGIMAlPALwB8SA9gJbB0C+A3ACgcZEmAAuHNiXg5CdTOWq1s8OGLIxpAZh4CBHHPEKoAdIYCEjeOQgQGWAfDRnCsunUE8gA

Changelog:
[Internal]

Reviewed By: jbrown215

Differential Revision: D17863358

fbshipit-source-id: 7689819de4c15f22e427cf5af520566bcea17bbc
---
 Libraries/Lists/VirtualizedSectionList.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Libraries/Lists/VirtualizedSectionList.js b/Libraries/Lists/VirtualizedSectionList.js
index 594165ba02c..29bd5fdda39 100644
--- a/Libraries/Lists/VirtualizedSectionList.js
+++ b/Libraries/Lists/VirtualizedSectionList.js
@@ -341,8 +341,9 @@ class VirtualizedSectionList<
     viewableItems: Array<ViewToken>,
     changed: Array<ViewToken>,
   }) => {
-    if (this.props.onViewableItemsChanged) {
-      this.props.onViewableItemsChanged({
+    const onViewableItemsChanged = this.props.onViewableItemsChanged;
+    if (onViewableItemsChanged != null) {
+      onViewableItemsChanged({
         viewableItems: viewableItems
           .map(this._convertViewable, this)
           .filter(Boolean),