implement null aware ops, fixes #249

lib/src/checker/checker.dart

 // Copyright (c) 2015, 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.
 
 library dev_compiler.src.checker.checker;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/scanner.dart' show Token, TokenType;
@@ skipping 371 matching lines @@
       final node = init[i];
       if (node is SuperConstructorInvocation) {
         _recordMessage(new InvalidSuperInvocation(node));
       }
     }
   }
 
   @override
   void visitConstructorFieldInitializer(ConstructorFieldInitializer node) {
     var field = node.fieldName;
-    DartType staticType = rules.elementType(field.staticElement);
+    var element = field.staticElement;
+    DartType staticType = rules.elementType(element);
     checkAssignment(node.expression, staticType);
     node.visitChildren(this);
   }
 
   @override
   void visitForEachStatement(ForEachStatement node) {
     // Check that the expression is an Iterable.
     var expr = node.iterable;
     var iterableType = node.awaitKeyword != null
         ? rules.provider.streamType
@@ skipping 382 matching lines @@
     } else {
       // Non-method operator.
       switch (op.type) {
         case TokenType.AMPERSAND_AMPERSAND:
         case TokenType.BAR_BAR:
           checkBoolean(node.leftOperand);
           checkBoolean(node.rightOperand);
           break;
         case TokenType.BANG_EQ:
           break;
+        case TokenType.QUESTION_QUESTION:
+          break;
         default:
           assert(false);
       }
     }
     node.visitChildren(this);
   }
 
   @override
   void visitConditionalExpression(ConditionalExpression node) {
     checkBoolean(node.condition);
@@ skipping 129 matching lines @@
     if (info is CoercionInfo) {
       // TODO(jmesserly): if we're run again on the same AST, we'll produce the
       // same annotations. This should be harmless. This might go away once
       // CodeChecker is integrated better with analyzer, as it will know that
       // checking has already been performed.
       // assert(CoercionInfo.get(info.node) == null);
       CoercionInfo.set(info.node, info);
     }
   }
 }