Void is not required to be `null` anymore.

pkg/compiler/lib/src/ssa/nodes.dart

Index: pkg/compiler/lib/src/ssa/nodes.dart
diff --git a/pkg/compiler/lib/src/ssa/nodes.dart b/pkg/compiler/lib/src/ssa/nodes.dart
index cfee3948caee0c1f3f23a606a37a095332983cab..7746f75e7f6699d24d1fbef4197ee1e74807ea94 100644
--- a/pkg/compiler/lib/src/ssa/nodes.dart
+++ b/pkg/compiler/lib/src/ssa/nodes.dart
@@ -1342,8 +1342,9 @@ abstract class HInstruction implements Spannable {
     assert(!type.isTypeVariable);
     assert(type.treatAsRaw || type.isFunctionType);
     if (type.isDynamic) return this;
+    if (type.isVoid) return this;
     if (type == closedWorld.commonElements.objectType) return this;
-    if (type.isVoid || type.isFunctionType || type.isMalformed) {
+    if (type.isFunctionType || type.isMalformed) {
       return new HTypeConversion(
           type, kind, closedWorld.commonMasks.dynamicType, this);
     }