Fix an exception caused by incomplete input (issue 29687)

pkg/analyzer/lib/src/summary/summarize_const_expr.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.
 
 library serialization.summarize_const_expr;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/type.dart' show DartType;
 import 'package:analyzer/src/summary/format.dart';
@@ skipping 268 matching lines @@
       strings.add(expr.prefix.name);
       operations.add(UnlinkedExprOperation.pushParameter);
       strings.add(expr.identifier.name);
       operations.add(UnlinkedExprOperation.assignToProperty);
     } else {
       throw new StateError('Unsupported assignable: $expr');
     }
   }
 
   void _pushInt(int value) {
+    if (value == null) {
+      value = 0;

[scheglov, 2017/05/30 17:25:18]

This could be also.

value ??= 0;

[Brian Wilkerson, 2017/05/30 17:38:45]

Done

+    }
     assert(value >= 0);
     if (value >= 0x100000000) {
       int numOfComponents = 0;
       ints.add(numOfComponents);
       void pushComponents(int value) {
         if (value >= 0x100000000) {
           pushComponents(value ~/ 0x100000000);
         }
         numOfComponents++;
         ints.add(value & 0xFFFFFFFF);
@@ skipping 390 matching lines @@
     if (typeArguments == null) {
       ints.add(0);
     } else {
       ints.add(typeArguments.arguments.length);
       for (TypeAnnotation type in typeArguments.arguments) {
         references.add(serializeTypeName(type));
       }
     }
   }
 }