Add missing returns. As of `1.18.0-dev-0`, these cases will get flagged. In the meantime, the

diff --git a/packages/flutter/lib/src/animation/animations.dart b/packages/flutter/lib/src/animation/animations.dart
index 4544231..537cee9 100644
--- a/packages/flutter/lib/src/animation/animations.dart
+++ b/packages/flutter/lib/src/animation/animations.dart

@@ -287,6 +287,7 @@
       case AnimationStatus.completed: return AnimationStatus.dismissed;
       case AnimationStatus.dismissed: return AnimationStatus.completed;
     }
+    return null;    
   }
 
   @override

diff --git a/packages/flutter/lib/src/cassowary/expression.dart b/packages/flutter/lib/src/cassowary/expression.dart
index 55742aa..4b36ee1 100644
--- a/packages/flutter/lib/src/cassowary/expression.dart
+++ b/packages/flutter/lib/src/cassowary/expression.dart

@@ -157,7 +157,6 @@
     if (!m.isConstant) {
       throw new ParserException(
           'The divisor was not a constant expression', <EquationMember>[this, m]);
-      return null;
     }
 
     return this._applyMultiplicand(1.0 / m.value);

diff --git a/packages/flutter/lib/src/material/button.dart b/packages/flutter/lib/src/material/button.dart
index c968743..efc4c84 100644
--- a/packages/flutter/lib/src/material/button.dart
+++ b/packages/flutter/lib/src/material/button.dart

@@ -227,6 +227,7 @@
           return Colors.white30;
       }
     }
+    return null;
   }
 
   void _handleHighlightChanged(bool value) {

diff --git a/packages/flutter/lib/src/material/dialog.dart b/packages/flutter/lib/src/material/dialog.dart
index 2a5e10c..4feae02 100644
--- a/packages/flutter/lib/src/material/dialog.dart
+++ b/packages/flutter/lib/src/material/dialog.dart

@@ -63,6 +63,7 @@
       case Brightness.dark:
         return Colors.grey[800];
     }
+    return null;
   }
 
   @override

diff --git a/packages/flutter/lib/src/material/drawer_item.dart b/packages/flutter/lib/src/material/drawer_item.dart
index 8963149..4f48ed8 100644
--- a/packages/flutter/lib/src/material/drawer_item.dart
+++ b/packages/flutter/lib/src/material/drawer_item.dart

@@ -67,6 +67,7 @@
           return Colors.white30;
         return null; // use default icon theme colour unmodified
     }
+    return null;  
   }
 
   TextStyle _getTextStyle(ThemeData themeData) {

diff --git a/packages/flutter/lib/src/material/icon.dart b/packages/flutter/lib/src/material/icon.dart
index a16e496..bc65bd1 100644
--- a/packages/flutter/lib/src/material/icon.dart
+++ b/packages/flutter/lib/src/material/icon.dart

@@ -65,6 +65,7 @@
       case Brightness.light:
         return Colors.black;
     }
+    return null;    
   }
 
   Color _getDefaultColor(BuildContext context) {

diff --git a/packages/flutter/lib/src/material/raised_button.dart b/packages/flutter/lib/src/material/raised_button.dart
index df7e24e..b01f048 100644
--- a/packages/flutter/lib/src/material/raised_button.dart
+++ b/packages/flutter/lib/src/material/raised_button.dart

@@ -104,6 +104,7 @@
         case Brightness.dark:
           return Colors.white12;
       }
+      return null;
     }
   }
 

diff --git a/packages/flutter/lib/src/material/text_selection.dart b/packages/flutter/lib/src/material/text_selection.dart
index 26e8054..f428c0f 100644
--- a/packages/flutter/lib/src/material/text_selection.dart
+++ b/packages/flutter/lib/src/material/text_selection.dart

@@ -186,4 +186,5 @@
         child: handle
       );
   }
+  return null;
 }

diff --git a/packages/flutter/lib/src/painting/box_painter.dart b/packages/flutter/lib/src/painting/box_painter.dart
index 6954c11..077a3c2 100644
--- a/packages/flutter/lib/src/painting/box_painter.dart
+++ b/packages/flutter/lib/src/painting/box_painter.dart

@@ -1353,6 +1353,7 @@
         double distance = (position - center).distance;
         return distance <= math.min(size.width, size.height) / 2.0;
     }
+    return null;
   }
 
   @override

diff --git a/packages/flutter/lib/src/painting/text_painter.dart b/packages/flutter/lib/src/painting/text_painter.dart
index face249..dd2408f 100644
--- a/packages/flutter/lib/src/painting/text_painter.dart
+++ b/packages/flutter/lib/src/painting/text_painter.dart

@@ -125,6 +125,7 @@
       case TextBaseline.ideographic:
         return _paragraph.ideographicBaseline;
     }
+    return null;
   }
 
   double _lastMinWidth;
@@ -211,6 +212,7 @@
             ?? _getOffsetFromUpstream(offset, caretPrototype)
             ?? emptyOffset;
     }
+    return null;
   }
 
   /// Returns a list of rects that bound the given selection.

diff --git a/packages/flutter/lib/src/rendering/box.dart b/packages/flutter/lib/src/rendering/box.dart
index 980f19b..c1ebd93 100644
--- a/packages/flutter/lib/src/rendering/box.dart
+++ b/packages/flutter/lib/src/rendering/box.dart

@@ -1125,7 +1125,6 @@
           'set a size and lay out any children, or, set sizedByParent to true '
           'so that performResize() sizes the render object.'
         );
-        return true;
       }
       return true;
     });

diff --git a/packages/flutter/lib/src/rendering/list.dart b/packages/flutter/lib/src/rendering/list.dart
index 25f51fd..a391ddc 100644
--- a/packages/flutter/lib/src/rendering/list.dart
+++ b/packages/flutter/lib/src/rendering/list.dart

@@ -82,6 +82,7 @@
       case Axis.horizontal:
         return padding.horizontal;
     }
+    return null;
   }
 
   double get _preferredExtent {

diff --git a/packages/flutter/lib/src/rendering/viewport.dart b/packages/flutter/lib/src/rendering/viewport.dart
index b3a7a47..9aa28b1 100644
--- a/packages/flutter/lib/src/rendering/viewport.dart
+++ b/packages/flutter/lib/src/rendering/viewport.dart

@@ -57,6 +57,7 @@
       case ViewportAnchor.end:
         return paintOffset + (containerSize - contentSize);
     }
+    return null;
   }
 
   @override

diff --git a/packages/flutter/lib/src/widgets/banner.dart b/packages/flutter/lib/src/widgets/banner.dart
index 55d06fc..be87827 100644
--- a/packages/flutter/lib/src/widgets/banner.dart
+++ b/packages/flutter/lib/src/widgets/banner.dart

@@ -112,6 +112,7 @@
       case BannerLocation.topLeft:
         return -math.PI / 4.0;
     }
+    return null;
   }
 }
 

diff --git a/packages/flutter/lib/src/widgets/dismissable.dart b/packages/flutter/lib/src/widgets/dismissable.dart
index fad3279..8133646 100644
--- a/packages/flutter/lib/src/widgets/dismissable.dart
+++ b/packages/flutter/lib/src/widgets/dismissable.dart

@@ -245,7 +245,6 @@
           return vy > _kMinFlingVelocity;
       }
     }
-    return false;
   }
 
   void _handleDragEnd(DragEndDetails details) {

diff --git a/packages/flutter/lib/src/widgets/lazy_block.dart b/packages/flutter/lib/src/widgets/lazy_block.dart
index 8b927cc..6b08e76 100644
--- a/packages/flutter/lib/src/widgets/lazy_block.dart
+++ b/packages/flutter/lib/src/widgets/lazy_block.dart

@@ -740,6 +740,7 @@
       case Axis.vertical:
         return new Offset(0.0, size.height);
     }
+    return null;    
   }
 
   static RenderBox _getNextWithin(_RenderLazyBlock block, RenderBox child) {

diff --git a/packages/flutter/lib/src/widgets/pageable_list.dart b/packages/flutter/lib/src/widgets/pageable_list.dart
index b572554..3e547f1 100644
--- a/packages/flutter/lib/src/widgets/pageable_list.dart
+++ b/packages/flutter/lib/src/widgets/pageable_list.dart

@@ -224,6 +224,7 @@
       case Axis.vertical:
         return box.size.height;
     }
+    return null;
   }
 
   @override

diff --git a/packages/flutter/lib/src/widgets/scrollable.dart b/packages/flutter/lib/src/widgets/scrollable.dart
index e2f386f..38fabce 100644
--- a/packages/flutter/lib/src/widgets/scrollable.dart
+++ b/packages/flutter/lib/src/widgets/scrollable.dart

@@ -285,6 +285,7 @@
       case ViewportAnchor.end:
         return pixelOffset;
     }
+    return null;
   }
 
   /// Convert a scrollOffset value to the number of pixels to which it corresponds.

diff --git a/packages/flutter/lib/src/widgets/scrollable_list.dart b/packages/flutter/lib/src/widgets/scrollable_list.dart
index 28dca19..875d133 100644
--- a/packages/flutter/lib/src/widgets/scrollable_list.dart
+++ b/packages/flutter/lib/src/widgets/scrollable_list.dart

@@ -239,6 +239,7 @@
         }
         break;
     }
+    return null;
   }
 
   @override

diff --git a/packages/flutter/lib/src/widgets/text_selection.dart b/packages/flutter/lib/src/widgets/text_selection.dart
index c08ea39..06124af 100644
--- a/packages/flutter/lib/src/widgets/text_selection.dart
+++ b/packages/flutter/lib/src/widgets/text_selection.dart

@@ -294,5 +294,6 @@
       case TextDirection.rtl:
         return rtlType;
     }
+    return null;
   }
 }

diff --git a/packages/flutter/lib/src/widgets/virtual_viewport.dart b/packages/flutter/lib/src/widgets/virtual_viewport.dart
index 2342db5..59985c8 100644
--- a/packages/flutter/lib/src/widgets/virtual_viewport.dart
+++ b/packages/flutter/lib/src/widgets/virtual_viewport.dart

@@ -70,6 +70,7 @@
       case ViewportAnchor.end:
         return scrollOffset;
     }
+    return null;    
   }
 
   /// Returns a two-dimensional representation of the scroll offset, accounting

diff --git a/packages/flutter/test/widget/render_object_widget_test.dart b/packages/flutter/test/widget/render_object_widget_test.dart
index a8228af..b64a48d 100644
--- a/packages/flutter/test/widget/render_object_widget_test.dart
+++ b/packages/flutter/test/widget/render_object_widget_test.dart

@@ -29,6 +29,7 @@
       case Orientation.portrait:
         return new BoxDecoration(backgroundColor: const Color(0xFF0000FF));
     }
+    return null;
   }
 
   @override

diff --git a/packages/flutter_tools/lib/src/application_package.dart b/packages/flutter_tools/lib/src/application_package.dart
index dcd55eb..2810901 100644
--- a/packages/flutter_tools/lib/src/application_package.dart
+++ b/packages/flutter_tools/lib/src/application_package.dart

@@ -134,6 +134,7 @@
     case TargetPlatform.linux_x64:
       return null;
   }
+  return null;
 }
 
 class ApplicationPackageStore {
@@ -156,5 +157,6 @@
       case TargetPlatform.linux_x64:
         return null;
     }
+    return null;
   }
 }

diff --git a/packages/flutter_tools/lib/src/build_info.dart b/packages/flutter_tools/lib/src/build_info.dart
index c8d600e..c599cba 100644
--- a/packages/flutter_tools/lib/src/build_info.dart
+++ b/packages/flutter_tools/lib/src/build_info.dart

@@ -53,6 +53,7 @@
       return 'linux-x64';
   }
   assert(false);
+  return null;
 }
 
 enum TargetPlatform {
@@ -80,6 +81,7 @@
       return 'linux-x64';
   }
   assert(false);
+  return null;
 }
 
 TargetPlatform getTargetPlatformForName(String platform) {

diff --git a/packages/flutter_tools/lib/src/ios/devices.dart b/packages/flutter_tools/lib/src/ios/devices.dart
index 603ebc1..75804dd 100644
--- a/packages/flutter_tools/lib/src/ios/devices.dart
+++ b/packages/flutter_tools/lib/src/ios/devices.dart

@@ -235,7 +235,6 @@
     } else {
       return false;
     }
-    return false;
   }
 
   @override