Infer Null for return type of functions with empty returns.

pkg/analyzer/lib/src/generated/resolver.dart

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index 5d90f3c03d3c59932fa4978a73d9d30a7cf213f9..8b6fbf711ef55de721391a5ed9a0d6d059222b0f 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -4208,9 +4208,6 @@ class InferenceContext {
     if (_returnStack.isNotEmpty && _inferredReturn.isNotEmpty) {
       DartType context = _returnStack.removeLast() ?? DynamicTypeImpl.instance;
       DartType inferred = _inferredReturn.removeLast();
-      if (inferred.isBottom || inferred.isDartCoreNull) {
-        return;
-      }
 
       if (_typeSystem.isSubtypeOf(inferred, context)) {
         setType(node, inferred);
@@ -4225,7 +4222,7 @@ class InferenceContext {
    */
   void pushReturnContext(BlockFunctionBody node) {
     _returnStack.add(getContext(node));
-    _inferredReturn.add(BottomTypeImpl.instance);
+    _inferredReturn.add(_typeProvider.nullType);
   }
 
   /**
@@ -9067,6 +9064,11 @@ abstract class TypeProvider {
   InterfaceType get futureNullType;
 
   /**
+   * Return the type representing 'FutureOr<Null>'.
+   */
+  InterfaceType get futureOrNullType;
+
+  /**
    * Return the type representing the built-in type 'FutureOr'.
    */
   InterfaceType get futureOrType;
@@ -9260,6 +9262,11 @@ class TypeProviderImpl extends TypeProviderBase {
   InterfaceType _futureNullType;
 
   /**
+   * The type representing 'FutureOr<Null>'.
+   */
+  InterfaceType _futureOrNullType;
+
+  /**
    * The type representing the built-in type 'FutureOr'.
    */
   InterfaceType _futureOrType;
@@ -9395,6 +9402,9 @@ class TypeProviderImpl extends TypeProviderBase {
   InterfaceType get futureNullType => _futureNullType;
 
   @override
+  InterfaceType get futureOrNullType => _futureOrNullType;
+
+  @override
   InterfaceType get futureOrType => _futureOrType;
 
   @override
@@ -9499,6 +9509,7 @@ class TypeProviderImpl extends TypeProviderBase {
     _undefinedType = UndefinedTypeImpl.instance;
     _futureDynamicType = _futureType.instantiate(<DartType>[_dynamicType]);
     _futureNullType = _futureType.instantiate(<DartType>[_nullType]);
+    _futureOrNullType = _futureOrType.instantiate(<DartType>[_nullType]);

[Paul Berry, 2017/02/07 18:13:03]

This line needs to be after line 9517, or a null reference exception will happen
when analyzer is used with old dart SDKs that lack FutureOr<T>.

Fix is here: https://codereview.chromium.org/2683683002

     _iterableDynamicType = _iterableType.instantiate(<DartType>[_dynamicType]);
     _streamDynamicType = _streamType.instantiate(<DartType>[_dynamicType]);
     // FutureOr<T> is still fairly new, so if we're analyzing an SDK that