Detect (null type == null type), and change it to true.

sdk/lib/_internal/compiler/implementation/ssa/optimize.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of ssa;
 
 abstract class OptimizationPhase {
   String get name;
   void visitGraph(HGraph graph);
 }
@@ skipping 470 matching lines @@
     HType leftType = left.instructionType;
     HType rightType = right.instructionType;
 
     // Intersection of int and double return conflicting, so
     // we don't optimize on numbers to preserve the runtime semantics.
     if (!(left.isNumberOrNull() && right.isNumberOrNull()) &&
         leftType.intersection(rightType, compiler).isConflicting()) {
       return graph.addConstantBool(false, constantSystem);
     }
 
+    if (left.isNull() && right.isNull()) {
+      return graph.addConstantBool(true, constantSystem);
+    }
+
     if (left.isConstantBoolean() && right.isBoolean()) {
       HConstant constant = left;
       if (constant.constant.isTrue()) {
         return right;
       } else {
         return new HNot(right);
       }
     }
 
     if (right.isConstantBoolean() && left.isBoolean()) {
@@ skipping 983 matching lines @@
     }
 
     // For other fields having setters in the generative constructor body, set
     // the type to UNKNOWN to avoid relying on the type set in the initializer
     // list.
     allSetters.forEach((Element element) {
       backend.registerFieldConstructor(element, HType.UNKNOWN);
     });
   }
 }