Infer Null for return type of functions with empty returns.

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

Index: pkg/analyzer/lib/src/generated/error_verifier.dart
diff --git a/pkg/analyzer/lib/src/generated/error_verifier.dart b/pkg/analyzer/lib/src/generated/error_verifier.dart
index 7285f1ddfb6387df20297d5895e88bae232f7763..00455ed019fc7493ddc58562d3b6b3a17200a4ac 100644
--- a/pkg/analyzer/lib/src/generated/error_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/error_verifier.dart
@@ -2306,7 +2306,10 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
             return;
           }
         }
-      } else if (expectedReturnType.isDynamic || expectedReturnType.isVoid) {
+      } else if (expectedReturnType.isDynamic ||
+          expectedReturnType.isVoid ||
+          _typeSystem.isSubtypeOf(
+              expectedReturnType, _typeProvider.futureOrNullType)) {

[Jennifer Messerly, 2017/02/03 18:47:53]

If I have:

    Future<Null> foo() {
      return;
    }

shouldn't that be a RETURN_WITHOUT_VALUE?

[Leaf, 2017/02/06 18:27:15]

Good catch, thanks!  Fixed to keep it simple for now.

         return;
       }
       _hasReturnWithoutValue = true;