Fix issue 2939, revert previous change that accepted null as excpetion objects:

runtime/vm/parser.cc

 // 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.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
@@ skipping 5154 matching lines @@
   // Now create a label for the end of catch block processing so that we can
   // jump over the catch block code after executing the try block.
   SourceLabel* end_catch_label =
       SourceLabel::New(token_index_, NULL, SourceLabel::kCatch);
 
   // Now parse the 'catch' blocks if any and merge all of them into
   // an if-then sequence of the different types specified using the 'is'
   // operator.
   bool catch_seen = false;
   bool generic_catch_seen = false;
-  intptr_t catch_clause_count = 0;
   SequenceNode* catch_handler_list = NULL;
   const intptr_t handler_pos = token_index_;
   OpenBlock();  // Start the catch block sequence.
   current_block_->scope->AddLabel(end_catch_label);
   while (CurrentToken() == Token::kCATCH) {
-    catch_clause_count++;
     catch_seen = true;
     const intptr_t catch_pos = token_index_;
     ConsumeToken();  // Consume the 'catch'.
     ExpectToken(Token::kLPAREN);
     CatchParamDesc exception_param;
     CatchParamDesc stack_trace_param;
     ParseCatchParameter(&exception_param);
     if (CurrentToken() == Token::kCOMMA) {
       ConsumeToken();
       ParseCatchParameter(&stack_trace_param);
@@ skipping 52 matching lines @@
       // the catch specifier.
       if (!exception_param.type->IsInstantiated() &&
           (current_block_->scope->function_level() > 0)) {
         // Make sure that the instantiator is captured.
         CaptureReceiver();
       }
       AstNode* exception_type = new TypeNode(catch_pos, *exception_param.type);
       AstNode* exception_var = new LoadLocalNode(catch_pos, *catch_excp_var);
       AstNode* type_cond_expr = new ComparisonNode(
           catch_pos, Token::kIS, exception_var, exception_type);
-      if (catch_clause_count == 1) {
-        // Null is also allowed, but check only in the first clause.
-        AstNode* null_literal =
-            new LiteralNode(catch_pos, Instance::ZoneHandle(Instance::null()));
-        AstNode* null_cond_expr = new ComparisonNode(
-            catch_pos, Token::kEQ_STRICT, exception_var, null_literal);
-        AstNode* or_node = new BinaryOpNode(
-            catch_pos, Token::kOR, null_cond_expr, type_cond_expr);
-        current_block_->statements->Add(
-            new IfNode(catch_pos, or_node, catch_handler, NULL));
-      } else {
-        current_block_->statements->Add(
-            new IfNode(catch_pos, type_cond_expr, catch_handler, NULL));
-      }
+      current_block_->statements->Add(
+          new IfNode(catch_pos, type_cond_expr, catch_handler, NULL));
     } else {
       // No exception type exists in the catch specifier so execute the
       // catch handler code unconditionally.
       current_block_->statements->Add(catch_handler);
       generic_catch_seen = true;
     }
     catch_clause = CloseBlock();
 
     // Add this individual catch handler to the catch handlers list.
     current_block_->statements->Add(catch_clause);
@@ skipping 3156 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart