Remove special casing of == null

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

 // Copyright (c) 2016, 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.
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart';
 import '../common.dart';
 import '../compiler.dart';
 import '../constants/expressions.dart';
@@ skipping 562 matching lines @@
   }
 
   TypeMask typeOfInvocation(ir.MethodInvocation send, ClosedWorld closedWorld) {
     ast.Node operatorNode = _astAdapter.kernel.nodeToAstOperator[send];
     if (operatorNode != null) {
       return _resultOf(_target).typeOfOperator(operatorNode);
     }
     if (send.name.name == '[]=') {
       return closedWorld.commonMasks.dynamicType;
     }
-    return _resultOf(_target).typeOfSend(_astAdapter.getNode(send));
+    ast.Node node = _astAdapter.getNodeOrNull(send);
+    if (node == null) {
+      assert(send.name.name == '==');
+      return closedWorld.commonMasks.dynamicType;
+    }
+    return _resultOf(_target).typeOfSend(node);
   }
 
   TypeMask typeOfGet(ir.PropertyGet getter) {
     return _resultOf(_target).typeOfSend(_astAdapter.getNode(getter));
   }
 
   TypeMask typeOfSet(ir.PropertySet setter, ClosedWorld closedWorld) {
     return closedWorld.commonMasks.dynamicType;
   }
 
@@ skipping 68 matching lines @@
   TypeMask selectorTypeOf(Selector selector, TypeMask mask) {
     return TypeMaskFactory.inferredTypeForSelector(
         selector, mask, _globalInferenceResults);
   }
 
   TypeMask typeFromNativeBehavior(
       native.NativeBehavior nativeBehavior, ClosedWorld closedWorld) {
     return TypeMaskFactory.fromNativeBehavior(nativeBehavior, closedWorld);
   }
 }