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

sdk/lib/_internal/compiler/implementation/ssa/nodes.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 HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
@@ skipping 820 matching lines @@
   bool isMutableArray() => instructionType.isMutableArray();
   bool isExtendableArray() => instructionType.isExtendableArray();
   bool isFixedArray() => instructionType.isFixedArray();
   bool isBoolean() => instructionType.isBoolean();
   bool isInteger() => instructionType.isInteger();
   bool isDouble() => instructionType.isDouble();
   bool isNumber() => instructionType.isNumber();
   bool isNumberOrNull() => instructionType.isNumberOrNull();
   bool isString() => instructionType.isString();
   bool isPrimitive() => instructionType.isPrimitive();
+  bool isNull() => instructionType.isNull();
   bool canBeNull() => instructionType.canBeNull();
   bool canBePrimitive(Compiler compiler) =>
       instructionType.canBePrimitive(compiler);
 
   bool isIndexable(Compiler compiler) =>
       instructionType.isIndexable(compiler);
   bool isMutableIndexable(Compiler compiler) =>
       instructionType.isMutableIndexable(compiler);
 
   // TODO(kasperl): Get rid of this one.
@@ skipping 1812 matching lines @@
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty);
     return statements.last.end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }