From e667b3c0972d1511a4af71c49e73077172b427c6 Mon Sep 17 00:00:00 2001
From: Ian Hickson <ian@hixie.ch>
Date: Sun, 25 Oct 2015 20:22:55 -0700
Subject: [PATCH] better feedback for null child to a Block or Column

Fixes #1687.
---
 packages/flutter/lib/src/widgets/framework.dart  | 6 ++++--
 packages/flutter/lib/src/widgets/scrollable.dart | 4 +++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/packages/flutter/lib/src/widgets/framework.dart b/packages/flutter/lib/src/widgets/framework.dart
index a3b6409d8d..3cbc44f59e 100644
--- a/packages/flutter/lib/src/widgets/framework.dart
+++ b/packages/flutter/lib/src/widgets/framework.dart
@@ -272,8 +272,10 @@ abstract class OneChildRenderObjectWidget extends RenderObjectWidget {
 /// storage for that child list, it doesn't actually provide the updating
 /// logic.)
 abstract class MultiChildRenderObjectWidget extends RenderObjectWidget {
-  const MultiChildRenderObjectWidget({ Key key, this.children })
-    : super(key: key);
+  MultiChildRenderObjectWidget({ Key key, this.children })
+    : super(key: key) {
+    assert(!children.any((Widget child) => child == null));
+  }
 
   final List<Widget> children;
 
diff --git a/packages/flutter/lib/src/widgets/scrollable.dart b/packages/flutter/lib/src/widgets/scrollable.dart
index a517dd5b3f..1ba5d39e9b 100644
--- a/packages/flutter/lib/src/widgets/scrollable.dart
+++ b/packages/flutter/lib/src/widgets/scrollable.dart
@@ -384,7 +384,9 @@ class Block extends StatelessComponent {
     this.initialScrollOffset,
     this.scrollDirection: ScrollDirection.vertical,
     this.onScroll
-  }) : super(key: key);
+  }) : super(key: key) {
+    assert(!children.any((Widget child) => child == null));
+  }
 
   final List<Widget> children;
   final double initialScrollOffset;