Fixes for AST summary generation when variables are missing.

pkg/analyzer/lib/src/summary/summarize_ast.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_ast;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
@@ skipping 840 matching lines @@
     Block oldBlock = enclosingBlock;
     enclosingBlock = node;
     super.visitBlock(node);
     enclosingBlock = oldBlock;
   }
 
   @override
   void visitCatchClause(CatchClause node) {
     SimpleIdentifier exception = node.exceptionParameter;
     SimpleIdentifier st = node.stackTraceParameter;
-    serializeDeclaredIdentifier(
-        node, null, null, false, false, node.exceptionType, false, exception);
+    if (exception != null) {
+      serializeDeclaredIdentifier(
+          node, null, null, false, false, node.exceptionType, false, exception);
+    }
     if (st != null) {
       serializeDeclaredIdentifier(
           node, null, null, false, false, null, false, st);
     }
     super.visitCatchClause(node);
   }
 
   @override
   void visitClassDeclaration(ClassDeclaration node) {
     TypeName superclass =
@@ skipping 153 matching lines @@
         loopVariable.isFinal,
         loopVariable.isConst,
         loopVariable.type,
         true,
         loopVariable.identifier);
     super.visitForEachStatement(node);
   }
 
   @override
   void visitForStatement(ForStatement node) {
-    serializeVariables(node, node.variables, false, null, null, false);
+    VariableDeclarationList declaredVariables = node.variables;
+    if (declaredVariables != null) {
+      serializeVariables(node, declaredVariables, false, null, null, false);
+    }
     super.visitForStatement(node);
   }
 
   @override
   void visitFunctionDeclaration(FunctionDeclaration node) {
     executables.add(serializeExecutable(
         node,
         node.name.name,
         node.name.offset,
         node.isGetter,
@@ skipping 183 matching lines @@
 /**
  * A [_TypeParameterScope] is a [_Scope] which defines [_ScopedTypeParameter]s.
  */
 class _TypeParameterScope extends _Scope {
   /**
    * Get the number of [_ScopedTypeParameter]s defined in this
    * [_TypeParameterScope].
    */
   int get length => _definedNames.length;
 }